diff --git a/README.md b/README.md
index 1e05cf5a..0607365b 100644
--- a/README.md
+++ b/README.md
@@ -4,11 +4,11 @@ Think Smalltalk in a Lua-sized package with a dash of Erlang and wrapped up in
 a familiar, modern [syntax][].
 
 ```dart
-IO.print("Hello, world!")
+System.print("Hello, world!")
 
 class Wren {
   flyTo(city) {
-    IO.print("Flying to ", city)
+    System.print("Flying to ", city)
   }
 }
 
@@ -16,7 +16,7 @@ var adjectives = Fiber.new {
   ["small", "clean", "fast"].each {|word| Fiber.yield(word) }
 }
 
-while (!adjectives.isDone) IO.print(adjectives.call())
+while (!adjectives.isDone) System.print(adjectives.call())
 ```
 
  *  **Wren is small.** The VM implementation is under [4,000 semicolons][src].
diff --git a/builtin/core.wren b/builtin/core.wren
index 77937448..dde36fcf 100644
--- a/builtin/core.wren
+++ b/builtin/core.wren
@@ -213,3 +213,38 @@ class MapValueSequence is Sequence {
 }
 
 class Range is Sequence {}
+
+class System {
+  static print() {
+    writeString_("\n")
+  }
+
+  static print(obj) {
+    writeObject_(obj)
+    writeString_("\n")
+    return obj
+  }
+
+  static printAll(sequence) {
+    for (object in sequence) writeObject_(object)
+    writeString_("\n")
+  }
+
+  static write(obj) {
+    writeObject_(obj)
+    return obj
+  }
+
+  static writeAll(sequence) {
+    for (object in sequence) writeObject_(object)
+  }
+
+  static writeObject_(obj) {
+    var string = obj.toString
+    if (string is String) {
+      writeString_(string)
+    } else {
+      writeString_("[invalid toString]")
+    }
+  }
+}
diff --git a/builtin/io.wren b/builtin/io.wren
deleted file mode 100644
index 6b8df735..00000000
--- a/builtin/io.wren
+++ /dev/null
@@ -1,101 +0,0 @@
-class IO {
-  static print {
-    writeString_("\n")
-  }
-
-  static print(obj) {
-    writeObject_(obj)
-    writeString_("\n")
-    return obj
-  }
-
-  static print(a1, a2) {
-    printAll([a1, a2])
-  }
-
-  static print(a1, a2, a3) {
-    printAll([a1, a2, a3])
-  }
-
-  static print(a1, a2, a3, a4) {
-    printAll([a1, a2, a3, a4])
-  }
-
-  static print(a1, a2, a3, a4, a5) {
-    printAll([a1, a2, a3, a4, a5])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6) {
-    printAll([a1, a2, a3, a4, a5, a6])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6, a7) {
-    printAll([a1, a2, a3, a4, a5, a6, a7])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6, a7, a8) {
-    printAll([a1, a2, a3, a4, a5, a6, a7, a8])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9) {
-    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10) {
-    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11) {
-    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12) {
-    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13) {
-    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14) {
-    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15) {
-    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15])
-  }
-
-  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16) {
-    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16])
-  }
-
-  static printAll(sequence) {
-    for (object in sequence) writeObject_(object)
-    writeString_("\n")
-  }
-
-  static write(obj) {
-    writeObject_(obj)
-    return obj
-  }
-
-  static read(prompt) {
-    if (!(prompt is String)) Fiber.abort("Prompt must be a string.")
-    write(prompt)
-    return read()
-  }
-
-  static writeObject_(obj) {
-    var string = obj.toString
-    if (string is String) {
-      writeString_(string)
-    } else {
-      writeString_("[invalid toString]")
-    }
-  }
-
-  foreign static writeString_(string)
-  foreign static clock
-  foreign static time
-  foreign static read()
-}
diff --git a/doc/site/classes.markdown b/doc/site/classes.markdown
index 60ca1631..a955e88c 100644
--- a/doc/site/classes.markdown
+++ b/doc/site/classes.markdown
@@ -25,7 +25,7 @@ To let our unicorn do stuff, we need to give it methods.
     :::dart
     class Unicorn {
       prance() {
-        IO.print("The unicorn prances in a fancy manner!")
+        System.print("The unicorn prances in a fancy manner!")
       }
     }
 
@@ -35,7 +35,7 @@ parameters, put their names inside the parentheses:
     :::dart
     class Unicorn {
       prance(where, when) {
-        IO.print("The unicorn prances in " + where + " at " + when)
+        System.print("The unicorn prances in " + where + " at " + when)
       }
     }
 
@@ -49,15 +49,15 @@ fine:
     :::dart
     class Unicorn {
       prance() {
-        IO.print("The unicorn prances in a fancy manner!")
+        System.print("The unicorn prances in a fancy manner!")
       }
 
       prance(where) {
-        IO.print("The unicorn prances in " + where)
+        System.print("The unicorn prances in " + where)
       }
 
       prance(where, when) {
-        IO.print("The unicorn prances in " + where + " at " + when)
+        System.print("The unicorn prances in " + where + " at " + when)
       }
     }
 
@@ -83,7 +83,7 @@ Many methods on a class exist to expose or compute some property of the object.
 For example:
 
     :::dart
-    IO.print("string".count) // "6".
+    System.print("string".count) // "6".
 
 These *getters* are just another kind of method—one without a parameter
 list. You can define them like so:
@@ -152,12 +152,12 @@ You can define operators in your class like so:
     class Unicorn {
       // Infix:
       +(other) {
-        IO.print("Adding to a unicorn?")
+        System.print("Adding to a unicorn?")
       }
 
       // Prefix:
       ! {
-        IO.print("Negating a unicorn?!")
+        System.print("Negating a unicorn?!")
       }
     }
 
@@ -191,7 +191,7 @@ like so:
     :::dart
     class Unicorn {
       construct new(name, color) {
-        IO.print("My name is " + name + " and I am " + color + ".")
+        System.print("My name is " + name + " and I am " + color + ".")
       }
     }
 
@@ -210,7 +210,7 @@ and each can clarify how it creates the instance:
     :::dart
     class Unicorn {
       construct brown(name) {
-        IO.print("My name is " + name + " and I am brown.")
+        System.print("My name is " + name + " and I am brown.")
       }
     }
 
@@ -326,13 +326,13 @@ not the instance. They can be used in *both* instance and static methods.
 Just like instance fields, static fields are initially `null`:
 
     :::dart
-    IO.print(Foo.bar) // null.
+    System.print(Foo.bar) // null.
 
 They can be used from static methods:
 
     :::dart
     Foo.set("foo")
-    IO.print(Foo.bar) // foo.
+    System.print(Foo.bar) // foo.
 
 And also instance methods. When you do so, there is still only one static field
 shared among all instances of the class:
@@ -342,7 +342,7 @@ shared among all instances of the class:
     var foo2 = Foo.new()
 
     foo1.setFromInstance("updated")
-    IO.print(foo2.baz) // updated.
+    System.print(foo2.baz) // updated.
 
 ## Inheritance
 
@@ -381,7 +381,7 @@ This also means constructors are not inherited:
     :::dart
     class Unicorn {
       this new(name) {
-        IO.print("My name is " + name + ".")
+        System.print("My name is " + name + ".")
       }
     }
 
@@ -398,7 +398,7 @@ This means you can do `super` calls inside a constructor:
     :::dart
     class Unicorn {
       this new(name) {
-        IO.print("My name is " + name + ".")
+        System.print("My name is " + name + ".")
       }
     }
 
diff --git a/doc/site/control-flow.markdown b/doc/site/control-flow.markdown
index 023082ca..e19a1624 100644
--- a/doc/site/control-flow.markdown
+++ b/doc/site/control-flow.markdown
@@ -31,7 +31,7 @@ The simplest branching statement, `if` lets you conditionally skip a chunk of
 code. It looks like this:
 
     :::dart
-    if (ready) IO.print("go!")
+    if (ready) System.print("go!")
 
 That evaluates the parenthesized expression after `if`. If it's true, then the
 statement after the condition is evaluated. Otherwise it is skipped. Instead of
@@ -39,23 +39,23 @@ a statement, you can have a [block](syntax.html#blocks):
 
     :::dart
     if (ready) {
-      IO.print("getSet")
-      IO.print("go!")
+      System.print("getSet")
+      System.print("go!")
     }
 
 You may also provide an `else` branch. It will be executed if the condition is
 false:
 
     :::dart
-    if (ready) IO.print("go!") else IO.print("not ready!")
+    if (ready) System.print("go!") else System.print("not ready!")
 
 And, of course, it can take a block too:
 
     :::dart
     if (ready) {
-      IO.print("go!")
+      System.print("go!")
     } else {
-      IO.print("not ready!")
+      System.print("not ready!")
     }
 
 ## While statements
@@ -100,7 +100,7 @@ That's what `for` is for. It looks like this:
 
     :::dart
     for (beatle in ["george", "john", "paul", "ringo"]) {
-      IO.print(beatle)
+      System.print(beatle)
     }
 
 A `for` loop has three components:
@@ -124,7 +124,7 @@ keyword all by itself. That will immediately exit out of the nearest enclosing
 
     :::dart
     for (i in [1, 2, 3, 4]) {
-      IO.print(i)
+      System.print(i)
       if (i == 3) break
     }
 
@@ -138,7 +138,7 @@ sequence of numbers, or loop a number of times. For that, you can create a
 
     :::dart
     for (i in 1..100) {
-      IO.print(i)
+      System.print(i)
     }
 
 This loops over the numbers from 1 to 100, including 100 itself. If you want to
@@ -146,7 +146,7 @@ leave off the last value, use three dots instead of two:
 
     :::dart
     for (i in 1...100) {
-      IO.print(i)
+      System.print(i)
     }
 
 This looks like some special "range" syntax in the `for` loop, but it's
@@ -168,7 +168,7 @@ When you write a loop like this:
 
     :::dart
     for (i in 1..100) {
-      IO.print(i)
+      System.print(i)
     }
 
 Wren sees it something like this:
@@ -178,7 +178,7 @@ Wren sees it something like this:
     var seq_ = 1..100
     while (iter_ = seq_.iterate(iter_)) {
       var i = seq_.iteratorValue(iter_)
-      IO.print(i)
+      System.print(i)
     }
 
 First, Wren evaluates the sequence expression and stores it in a hidden
diff --git a/doc/site/core/bool.markdown b/doc/site/core/bool.markdown
index fc5b991b..d1abb889 100644
--- a/doc/site/core/bool.markdown
+++ b/doc/site/core/bool.markdown
@@ -9,10 +9,9 @@ Boolean values. There are two instances, `true` and `false`.
 
 Returns the logical complement of the value.
 
-    > !true
-    false
-    > !false
-    true
+    :::dart
+    System.print(!true) // "false".
+    System.print(!false) // "true".
 
 ### toString
 
diff --git a/doc/site/core/class.markdown b/doc/site/core/class.markdown
index b26a827b..2d81afc0 100644
--- a/doc/site/core/class.markdown
+++ b/doc/site/core/class.markdown
@@ -15,14 +15,14 @@ The superclass of this class.
     class Crustacean {}
     class Crab is Crustacean {}
 
-    IO.print(Crab.supertype)        // "Crustacean"
+    System.print(Crab.supertype) // "Crustacean".
 
 A class with no explicit superclass implicitly inherits Object:
 
     :::dart
-    IO.print(Crustacean.supertype)  // "Object"
+    System.print(Crustacean.supertype) // "Object".
 
 Object forms the root of the class hierarchy and has no supertype:
 
     :::dart
-    IO.print(Object.supertype)  // "null"
+    System.print(Object.supertype) // "null".
diff --git a/doc/site/core/fiber.markdown b/doc/site/core/fiber.markdown
index 0791127e..5add46fa 100644
--- a/doc/site/core/fiber.markdown
+++ b/doc/site/core/fiber.markdown
@@ -10,7 +10,7 @@ fiber is run. Does not immediately start running the fiber.
 
     :::dart
     var fiber = Fiber.new {
-      IO.print("I won't get printed")
+      System.print("I won't get printed")
     }
 
 ## Static Methods
@@ -34,14 +34,14 @@ here means the last fiber that was started using `call` and not `run`.
 
     :::dart
     var fiber = Fiber.new {
-      IO.print("Before yield")
+      System.print("Before yield")
       Fiber.yield()
-      IO.print("After yield")
+      System.print("After yield")
     }
 
-    fiber.call()            // "Before yield"
-    IO.print("After call")  // "After call"
-    fiber.call()            // "After yield"
+    fiber.call()                // "Before yield"
+    System.print("After call")  // "After call"
+    fiber.call()                // "After yield"
 
 When resumed, the parent fiber's `call()` method returns `null`.
 
@@ -50,7 +50,7 @@ If a yielded fiber is resumed by calling `call()` or `run()` with an argument,
 
     :::dart
     var fiber = Fiber.new {
-      IO.print(Fiber.yield()) // "value"
+      System.print(Fiber.yield()) // "value"
     }
 
     fiber.call()        // Run until the first yield.
@@ -65,7 +65,7 @@ later.
 
     :::dart
     Fiber.yield()
-    IO.print("this does not get reached")
+    System.print("this does not get reached")
 
 ### Fiber.**yield**(value)
 
@@ -77,7 +77,7 @@ Similar to `Fiber.yield` but provides a value to return to the parent fiber's
       Fiber.yield("value")
     }
 
-    IO.print(fiber.call()) // "value"
+    System.print(fiber.call()) // "value"
 
 ## Methods
 
@@ -87,9 +87,9 @@ Starts or resumes the fiber if it is in a paused state.
 
     :::dart
     var fiber = Fiber.new {
-      IO.print("Fiber called")
+      System.print("Fiber called")
       Fiber.yield()
-      IO.print("Fiber called again")
+      System.print("Fiber called again")
     }
 
     fiber.call() // Start it.
@@ -103,7 +103,7 @@ If the called fiber is resuming from a yield, the `yield()` method returns
 
     :::dart
     var fiber = Fiber.new {
-      IO.print(Fiber.yield())
+      System.print(Fiber.yield())
     }
 
     fiber.call()
@@ -116,7 +116,7 @@ Invokes the fiber or resumes the fiber if it is in a paused state and sets
 
     :::dart
     var fiber = Fiber.new {
-      IO.print(Fiber.yield())
+      System.print(Fiber.yield())
     }
 
     fiber.call()
diff --git a/doc/site/core/fn.markdown b/doc/site/core/fn.markdown
index df62d26c..6ef32684 100644
--- a/doc/site/core/fn.markdown
+++ b/doc/site/core/fn.markdown
@@ -13,7 +13,7 @@ argument](../functions.html#block-arguments) to some other method.
 
     :::dart
     var fn = Fn.new {
-      IO.print("The body")
+      System.print("The body")
     }
 
 It is a runtime error if `function` is not a function.
@@ -25,8 +25,8 @@ It is a runtime error if `function` is not a function.
 The number of arguments the function requires.
 
     :::dart
-    IO.print(Fn.new {}.arity)             // 0.
-    IO.print(Fn.new {|a, b, c| a }.arity) // 3.
+    System.print(Fn.new {}.arity)             // 0.
+    System.print(Fn.new {|a, b, c| a }.arity) // 3.
 
 ### **call**(args...)
 
@@ -34,7 +34,7 @@ Invokes the function with the given arguments.
 
     :::dart
     var fn = Fn.new { |arg|
-      IO.print(arg)
+      System.print(arg)
     }
 
     fn.call("Hello world") // Prints "Hello world".
diff --git a/doc/site/core/index.markdown b/doc/site/core/index.markdown
index 7a94d84c..f592d394 100644
--- a/doc/site/core/index.markdown
+++ b/doc/site/core/index.markdown
@@ -20,6 +20,6 @@ All Wren source files automatically have access to the following classes:
 * [Range](range.html)
 * [Sequence](sequence.html)
 * [String](string.html)
-* [IO](io.html)
+* [System](system.html)
 
 [embedding]: ../embedding-api.html
diff --git a/doc/site/core/io.markdown b/doc/site/core/io.markdown
deleted file mode 100644
index 054eaf4e..00000000
--- a/doc/site/core/io.markdown
+++ /dev/null
@@ -1,60 +0,0 @@
-^title IO Class
-^category core
-
-The IO class can be used to read and write to and from the console.
-
-## Static Methods
-
-### IO.**print**(objects...)
-
-Prints a series of objects to the console followed by a newline. Each object is
-converted to a string by calling `toString` on it. This is overloaded to
-support up to 16 objects. To pass more, use `printAll()`.
-
-  > IO.print("I like bananas")
-  I like bananas
-  > IO.print("Oranges", 10)
-  Oranges10
-
-### IO.**printAll**(sequence)
-
-Iterates over [sequence] and prints each element, then prints a single newline
-at the end. Each element is converted to a string by calling `toString` on it.
-
-  > IO.printAll([1, [2, 3], 4])
-  1[2, 3]4
-
-### IO.**write**(object)
-
-Prints a single value to the console, but does not print a newline character
-afterwards. Converts the value to a string by calling `toString` on it.
-
-  > IO.write(4 + 5)
-  9>
-
-In the above example, the result of `4 + 5` is printed, and then the prompt is
-printed on the same line because no newline character was printed afterwards.
-
-### IO.**read**()
-
-Reads in a line of text from stdin. Note that the returned text includes the
-trailing newline.
-
-  > var name = IO.read()
-  John
-  > IO.print("Hello " + name + "!")
-  Hello John
-  !
-  >
-
-### IO.**read**(prompt)
-
-Displays `prompt` then reads in a line of text from stdin. Note that the
-returned text includes the trailing newline.
-
-  > var name = IO.read("Enter your name: ")
-  Enter your name: John
-  > IO.print("Hello " + name + "!")
-  Hello John
-  !
-  >
diff --git a/doc/site/core/list.markdown b/doc/site/core/list.markdown
index 6de35b7b..ec75a651 100644
--- a/doc/site/core/list.markdown
+++ b/doc/site/core/list.markdown
@@ -26,14 +26,14 @@ Inserts the `item` at `index` in the list.
     :::dart
     var list = ["a", "b", "c", "d"]
     list.insert(1, "e")
-    IO.print(list) // "[a, e, b, c, d]"
+    System.print(list) // "[a, e, b, c, d]".
 
 The `index` may be one past the last index in the list to append an element.
 
     :::dart
     var list = ["a", "b", "c"]
     list.insert(3, "d")
-    IO.print(list) // "[a, b, c, d]"
+    System.print(list) // "[a, b, c, d]".
 
 If `index` is negative, it counts backwards from the end of the list. It bases this on the length of the list *after* inserted the element, so that `-1` will append the element, not insert it before the last element.
 
@@ -41,12 +41,12 @@ If `index` is negative, it counts backwards from the end of the list. It bases t
     var list = ["a", "b"]
     list.insert(-1, "d")
     list.insert(-2, "c")
-    IO.print(list) // "[a, b, c, d]"
+    System.print(list) // "[a, b, c, d]".
 
 Returns the inserted item.
 
     :::dart
-    IO.print(["a", "c"].insert(1, "b")) // "b".
+    System.print(["a", "c"].insert(1, "b")) // "b".
 
 It is a runtime error if the index is not an integer or is out of bounds.
 
@@ -64,11 +64,11 @@ are shifted up to fill in where the removed element was.
     :::dart
     var list = ["a", "b", "c", "d"]
     list.removeAt(1)
-    IO.print(list) // "[a, c, d]".
+    System.print(list) // "[a, c, d]".
 
 Returns the removed item.
 
-    IO.print(["a", "b", "c"].removeAt(1)) // "b".
+    System.print(["a", "b", "c"].removeAt(1)) // "b".
 
 It is a runtime error if the index is not an integer or is out of bounds.
 
@@ -79,7 +79,7 @@ the end of the list where `-1` is the last element.
 
     :::dart
     var list = ["a", "b", "c"]
-    IO.print(list[1]) // "b".
+    System.print(list[1]) // "b".
 
 It is a runtime error if the index is not an integer or is out of bounds.
 
@@ -91,6 +91,6 @@ backwards from the end of the list where `-1` is the last element.
     :::dart
     var list = ["a", "b", "c"]
     list[1] = "new"
-    IO.print(list) // "[a, new, c]".
+    System.print(list) // "[a, new, c]".
 
 It is a runtime error if the index is not an integer or is out of bounds.
diff --git a/doc/site/core/map.markdown b/doc/site/core/map.markdown
index b5ef691d..16e814f3 100644
--- a/doc/site/core/map.markdown
+++ b/doc/site/core/map.markdown
@@ -50,8 +50,8 @@ map, returns `null`.
 
     :::dart
     var map = {"george": "harrison", "ringo": "starr"}
-    IO.print(map["ringo"]) // "starr".
-    IO.print(map["pete"])  // "null".
+    System.print(map["ringo"]) // "starr".
+    System.print(map["pete"])  // "null".
 
 ### **[**key**]=**(value) operator
 
diff --git a/doc/site/core/null.markdown b/doc/site/core/null.markdown
index 4bca4ff9..033a008e 100644
--- a/doc/site/core/null.markdown
+++ b/doc/site/core/null.markdown
@@ -7,5 +7,5 @@
 
 Returns `true`, since `null` is considered [false](../control-flow.html#truth).
 
-    > !null
-    true
+    :::dart
+    System.print(!null) // "true".
diff --git a/doc/site/core/num.markdown b/doc/site/core/num.markdown
index b617b374..baf86a81 100644
--- a/doc/site/core/num.markdown
+++ b/doc/site/core/num.markdown
@@ -132,9 +132,9 @@ from the beginning number to the ending number.
 
     :::dart
     var range = 1.2..3.4
-    IO.print(range.min)         // 1.2
-    IO.print(range.max)         // 3.4
-    IO.print(range.isInclusive) // true
+    System.print(range.min)         // 1.2
+    System.print(range.max)         // 3.4
+    System.print(range.isInclusive) // true
 
 ### **...**(other) operator
 
@@ -143,6 +143,6 @@ from the beginning number to the ending number not including the ending number.
 
     :::dart
     var range = 1.2...3.4
-    IO.print(range.min)         // 1.2
-    IO.print(range.max)         // 3.4
-    IO.print(range.isInclusive) // false
+    System.print(range.min)         // 1.2
+    System.print(range.max)         // 3.4
+    System.print(range.isInclusive) // false
diff --git a/doc/site/core/sequence.markdown b/doc/site/core/sequence.markdown
index c80061b9..3a783f3d 100644
--- a/doc/site/core/sequence.markdown
+++ b/doc/site/core/sequence.markdown
@@ -59,7 +59,7 @@ and counting the number of times the returned value evaluates to `true`.
 Iterates over the sequence, passing each element to the given `function`.
 
     :::dart
-    ["one", "two", "three"].each {|word| IO.print(word) }
+    ["one", "two", "three"].each {|word| System.print(word) }
 
 ### **isEmpty**
 
@@ -88,7 +88,7 @@ original sequence while it is iterated.
     :::dart
     var doubles = [1, 2, 3].map {|n| n * 2 }
     for (n in doubles) {
-      IO.print(n) // "2", "4", "6".
+      System.print(n) // "2", "4", "6".
     }
 
 The returned sequence is *lazy*. It only applies the mapping when you iterate
@@ -105,7 +105,7 @@ To force eager evaluation, just call `.toList` on the result.
     var numbers = [1, 2, 3]
     var doubles = numbers.map {|n| n * 2 }.toList
     numbers.add(4)
-    IO.print(doubles) // [2, 4, 6].
+    System.print(doubles) // [2, 4, 6].
 
 ### **reduce**(function)
 
@@ -142,7 +142,7 @@ function `predicate`. If it returns `false`, the element is skipped.
     :::dart
     var odds = (1..10).where {|n| n % 2 == 1 }
     for (n in odds) {
-      IO.print(n) // "1", "3", "5", "7", "9".
+      System.print(n) // "1", "3", "5", "7", "9".
     }
 
 The returned sequence is *lazy*. It only applies the filtering when you iterate
@@ -160,4 +160,4 @@ To force eager evaluation, just call `.toList` on the result.
     var numbers = [1, 2, 3, 4, 5, 6]
     var odds = numbers.where {|n| n % 2 == 1 }.toList
     numbers.add(7)
-    IO.print(odds) // [1, 3, 5].
+    System.print(odds) // [1, 3, 5].
diff --git a/doc/site/core/string.markdown b/doc/site/core/string.markdown
index 2c68a7d9..8ada08ca 100644
--- a/doc/site/core/string.markdown
+++ b/doc/site/core/string.markdown
@@ -37,7 +37,7 @@ on strings *return* byte indexes too. So, for example, this does what you want:
     :::dart
     var metalBand = "Fäcëhämmër"
     var hPosition = metalBand.indexOf("h")
-    IO.print(metalBand[hPosition]) // "h"
+    System.print(metalBand[hPosition]) // "h"
 
 If you want to work with a string as a sequence numeric code points, call the
 `codePoints` getter. It returns a [Sequence](sequence.html) that decodes UTF-8
@@ -68,7 +68,7 @@ methods, the returned object also has a subscript operator that can be used to
 directly index bytes.
 
     :::dart
-    IO.print("hello".bytes[1]) // 101, for "e".
+    System.print("hello".bytes[1]) // 101, for "e".
 
 The `count` method on the returned sequence returns the number of bytes in the
 string. Unlike `count` on the string itself, it does not have to iterate over
@@ -83,15 +83,15 @@ single-character strings, this returns the numeric code point values.
 
     :::dart
     var string = "(ᵔᴥᵔ)"
-    IO.print(string.codePoints[0]) // 40, for "(".
-    IO.print(string.codePoints[4]) // 7461, for "ᴥ".
+    System.print(string.codePoints[0]) // 40, for "(".
+    System.print(string.codePoints[4]) // 7461, for "ᴥ".
 
 If the byte at `index` does not begin a valid UTF-8 sequence, or the end of the
 string is reached before the sequence is complete, returns `-1`.
 
     :::dart
     var string = "(ᵔᴥᵔ)"
-    IO.print(string.codePoints[2]) // -1, in the middle of "ᵔ".
+    System.print(string.codePoints[2]) // -1, in the middle of "ᵔ".
 
 ### **contains**(other)
 
@@ -132,7 +132,7 @@ for iterating over the *code points* in the string:
       codePoints.add(c)
     }
 
-    IO.print(codePoints) // ["(", "ᵔ", "ᴥ", "ᵔ", ")"].
+    System.print(codePoints) // ["(", "ᵔ", "ᴥ", "ᵔ", ")"].
 
 If the string contains any bytes that are not valid UTF-8, this iterates over
 those too, one byte at a time.
@@ -162,7 +162,7 @@ Check if the string is not equal to `other`.
 Returns a string containing the code point starting at byte `index`.
 
     :::dart
-    IO.print("ʕ•ᴥ•ʔ"[5]) // "ᴥ".
+    System.print("ʕ•ᴥ•ʔ"[5]) // "ᴥ".
 
 Since `ʕ` is two bytes in UTF-8 and `•` is three, the fifth byte points to the
 bear's nose.
@@ -171,7 +171,7 @@ If `index` points into the middle of a UTF-8 sequence or at otherwise invalid
 UTF-8, this returns a one-byte string containing the byte at that index:
 
     :::dart
-    IO.print("I ♥ NY"[3]) // One-byte string whose value is 153.
+    System.print("I ♥ NY"[3]) // One-byte string whose value is 153.
 
 It is a runtime error if `index` is greater than the number of bytes in the
 string.
diff --git a/doc/site/core/system.markdown b/doc/site/core/system.markdown
new file mode 100644
index 00000000..cbc4b081
--- /dev/null
+++ b/doc/site/core/system.markdown
@@ -0,0 +1,43 @@
+^title System Class
+^category core
+
+The System class is a grab-bag of functionality exposed by the VM, mostly for
+use during development or debugging.
+
+## Static Methods
+
+### System.**print**()
+
+Prints a single newline to the console.
+
+### System.**print**(object)
+
+Prints [object] to the console followed by a newline. If not already a string,
+the object is converted to a string by calling `toString` on it.
+
+    :::dart
+    System.print("I like bananas") // Prints "I like bananas".
+
+### System.**printAll**(sequence)
+
+Iterates over [sequence] and prints each element, then prints a single newline
+at the end. Each element is converted to a string by calling `toString` on it.
+
+    :::dart
+    System.printAll([1, [2, 3], 4]) // Prints "1[2, 3]4".
+
+### System.**write**(object)
+
+Prints a single value to the console, but does not print a newline character
+afterwards. Converts the value to a string by calling `toString` on it.
+
+    :::dart
+    System.write(4 + 5) // Prints "9".
+
+In the above example, the result of `4 + 5` is printed, and then the prompt is
+printed on the same line because no newline character was printed afterwards.
+
+### System.**clock**
+
+Returns the number of seconds (including fractional seconds) since the program
+was started. This is usually used for benchmarking.
diff --git a/doc/site/embedding-api.markdown b/doc/site/embedding-api.markdown
index 2a7cb0a4..cb09a721 100644
--- a/doc/site/embedding-api.markdown
+++ b/doc/site/embedding-api.markdown
@@ -70,7 +70,7 @@ You can tell the VM to execute a string of Wren source code like so:
     :::c
     WrenInterpretResult result = wrenInterpret(vm,
         "<where>",
-        "IO.print(\"Hi!\")");
+        "System.print(\"Hi!\")");
 
 The first string parameter is a "source path". It's just an arbitrary string that describes where the source code is from. It's what shows up in stack traces if a runtime error occurs in the code. It can be whatever you want as long as it's not `NULL`.
 
diff --git a/doc/site/error-handling.markdown b/doc/site/error-handling.markdown
index e0271e8a..b852ff86 100644
--- a/doc/site/error-handling.markdown
+++ b/doc/site/error-handling.markdown
@@ -108,7 +108,7 @@ For example, if you run this program:
     }
 
     var error = fiber.try()
-    IO.print("Caught error: ", error)
+    System.print("Caught error: " + error)
 
 It prints:
 
@@ -120,7 +120,7 @@ usual. When a fiber has been aborted because of a runtime error, you can also
 get the error from the fiber object. Continuing the above example:
 
     :::dart
-    IO.print(fiber.error)
+    System.print(fiber.error)
 
 This also prints:
 
diff --git a/doc/site/expressions.markdown b/doc/site/expressions.markdown
index a7a84abb..e083fda6 100644
--- a/doc/site/expressions.markdown
+++ b/doc/site/expressions.markdown
@@ -29,7 +29,7 @@ Wren is object-oriented, so most code consists of method calls. Most of them
 look like so:
 
     :::dart
-    IO.print("hello")
+    System.print("hello")
     items.add("another")
     items.insert(1, "value")
 
@@ -61,7 +61,7 @@ argument](functions.html#block-arguments):
 
     :::dart
     blondie.callMeAt(867, 5309) {
-      IO.print("This is the body!")
+      System.print("This is the body!")
     }
 
 Semantically, all method calls work like so:
@@ -98,7 +98,7 @@ call:
     :::dart
     class Base {
       method {
-        IO.print("base method")
+        System.print("base method")
       }
     }
 
@@ -114,7 +114,7 @@ base class constructor:
     :::dart
     class Base {
       this new(arg) {
-        IO.print("base constructor got ", arg)
+        System.print("base constructor got " + arg)
       }
     }
 
@@ -218,16 +218,16 @@ A `&&` ("logical and") expression evaluates the left-hand argument. If it's
 and returns the right-hand argument.
 
     :::dart
-    IO.print(false && 1)  // false
-    IO.print(1 && 2)      // 2
+    System.print(false && 1)  // false
+    System.print(1 && 2)      // 2
 
 An `||` ("logical or") expression is reversed. If the left-hand argument is
 [true](control-flow.html#truth), it's returned, otherwise the right-hand
 argument is evaluated and returned:
 
     :::dart
-    IO.print(false || 1)  // 1
-    IO.print(1 || 2)      // 1
+    System.print(false || 1)  // 1
+    System.print(1 || 2)      // 1
 
 ## The conditional operator `?:`
 
@@ -236,7 +236,7 @@ the little "if statement in the form of an expression" you know and love from C
 and its brethren.
 
     :::dart
-    IO.print(1 != 2 ? "math is sane" : "math is not sane!")
+    System.print(1 != 2 ? "math is sane" : "math is not sane!")
 
 It takes a condition expression, followed by `?`, followed by a then
 expression, a `:`, then an else expression. Just like `if`, it evaluates the
diff --git a/doc/site/fibers.markdown b/doc/site/fibers.markdown
index addd8c93..b1899a6e 100644
--- a/doc/site/fibers.markdown
+++ b/doc/site/fibers.markdown
@@ -28,7 +28,7 @@ using the `Fiber` class's constructor:
 
     :::dart
     var fiber = Fiber.new {
-      IO.print("This runs in a separate fiber.")
+      System.print("This runs in a separate fiber.")
     }
 
 Creating a fiber does not immediately run it. It's just a first class bundle of
@@ -48,7 +48,7 @@ until it passes control to another fiber. If it reaches the end of its body,
 it's considered *done*:
 
     :::dart
-    var fiber = Fiber.new { IO.print("Hi") }
+    var fiber = Fiber.new { System.print("Hi") }
     fiber.isDone // false
     fiber.call()
     fiber.isDone // true
@@ -71,16 +71,16 @@ You can make a fiber yield by calling the static `yield()` method on `Fiber`:
 
     :::dart
     var fiber = Fiber.new {
-      IO.print("fiber 1")
+      System.print("fiber 1")
       Fiber.yield()
-      IO.print("fiber 2")
+      System.print("fiber 2")
     }
 
-    IO.print("main 1")
+    System.print("main 1")
     fiber.call()
-    IO.print("main 2")
+    System.print("main 2")
     fiber.call()
-    IO.print("main 3")
+    System.print("main 3")
 
 This program prints:
 
@@ -105,7 +105,7 @@ of the `yield()` call:
     :::dart
     var fiber = Fiber.new {
       var result = Fiber.yield()
-      IO.print(result)
+      System.print(result)
     }
 
     fiber.call("discarded")
@@ -124,7 +124,7 @@ invoke the fiber:
       Fiber.yield("sent")
     }
 
-    IO.print(fiber.call())
+    System.print(fiber.call())
 
 This also prints "sent".
 
diff --git a/doc/site/functions.markdown b/doc/site/functions.markdown
index 6d753fb1..85bf6f4c 100644
--- a/doc/site/functions.markdown
+++ b/doc/site/functions.markdown
@@ -22,7 +22,7 @@ a method. At its simplest, it looks like this:
 
     :::dart
     blondie.callMe {
-      IO.print("This is the body!")
+      System.print("This is the body!")
     }
 
 Here we're invoking the `callMe` method on `blondie`. We're passing one
@@ -44,7 +44,7 @@ the block just like a regular argument list. For example:
 
     :::dart
     blondie.callMeAt(867, 5309) {
-      IO.print("This is the body!")
+      System.print("This is the body!")
     }
 
 Of course, you don't *have* to use a block argument to pass a function to a
@@ -62,7 +62,7 @@ class's constructor:
 
     :::dart
     var someFn = Fn.new {
-      IO.print("Hi!")
+      System.print("Hi!")
     }
 
 As you can see it takes a block argument too! All the constructor does it
@@ -87,7 +87,7 @@ method is dynamically-dispatched like any other, so you can define your own
     :::dart
     class FakeFn {
       call() {
-        IO.print("I'm feeling functional!")
+        System.print("I'm feeling functional!")
       }
     }
 
@@ -102,7 +102,7 @@ of the body, like so:
 
     :::dart
     blondie.callMe {|first, last|
-      IO.print("Hi, " + first + " " + last + "!")
+      System.print("Hi, " + first + " " + last + "!")
     }
 
 Here we're passing a function to `greet` that takes two parameters, `first` and
@@ -157,6 +157,6 @@ to`i`:
 
     :::dart
     var counter = Counter.create
-    IO.print(counter.call()) // Prints "1".
-    IO.print(counter.call()) // Prints "2".
-    IO.print(counter.call()) // Prints "3".
+    System.print(counter.call()) // Prints "1".
+    System.print(counter.call()) // Prints "2".
+    System.print(counter.call()) // Prints "3".
diff --git a/doc/site/getting-started.markdown b/doc/site/getting-started.markdown
index ecf22793..5b1fedc3 100644
--- a/doc/site/getting-started.markdown
+++ b/doc/site/getting-started.markdown
@@ -49,12 +49,12 @@ interactive mode. You can type in a line of code, and it will immediately
 execute it. Here's something to try:
 
     :::dart
-    IO.print("Hello, world!")
+    System.print("Hello, world!")
 
 Or a little more exciting:
 
     :::dart
-    for (i in 1..10) IO.print("Counting up ", i)
+    for (i in 1..10) System.print("Counting up " + i.toString)
 
 You can exit the interpreter using good old Ctrl-C or Ctrl-D, or just throw
 your computer to the ground and storm off.
@@ -80,10 +80,10 @@ your favorite text editor and paste this into it:
           y0 = y1
           iter = iter + 1
         }
-        IO.write(" .-:;+=xX$& "[iter])
+        System.write(" .-:;+=xX$& "[iter])
       }
 
-      IO.print("")
+      System.print("")
     }
 
 Now run:
diff --git a/doc/site/index.markdown b/doc/site/index.markdown
index 9df5669c..e6ecc716 100644
--- a/doc/site/index.markdown
+++ b/doc/site/index.markdown
@@ -6,11 +6,11 @@ Think Smalltalk in a Lua-sized package with a dash of Erlang and wrapped up in
 a familiar, modern [syntax][].
 
     :::dart
-    IO.print("Hello, world!")
+    System.print("Hello, world!")
 
     class Wren {
       flyTo(city) {
-        IO.print("Flying to ", city)
+        System.print("Flying to " + city)
       }
     }
 
@@ -18,7 +18,7 @@ a familiar, modern [syntax][].
       ["small", "clean", "fast"].each {|word| Fiber.yield(word) }
     }
 
-    while (!adjectives.isDone) IO.print(adjectives.call())
+    while (!adjectives.isDone) System.print(adjectives.call())
 
  *  **Wren is small.** The VM implementation is under [4,000 semicolons][src].
     You can skim the whole thing in an afternoon. It's *small*, but not
diff --git a/doc/site/lists.markdown b/doc/site/lists.markdown
index 5b71a8fc..42a3cb7d 100644
--- a/doc/site/lists.markdown
+++ b/doc/site/lists.markdown
@@ -59,14 +59,14 @@ existing element in the list using the subscript setter:
 
     :::dart
     hirsute[1] = "muttonchops"
-    IO.print(hirsute[1]) // muttonchops.
+    System.print(hirsute[1]) // muttonchops.
 
 It's an error to set an element that's out of bounds. To grow a list, you can
 use `add` to append a single item to the end:
 
     :::dart
     hirsute.add("goatee")
-    IO.print(hirsute.count) // 4.
+    System.print(hirsute.count) // 4.
 
 You can insert a new element at a specific position using `insert`:
 
@@ -84,9 +84,9 @@ back. Doing so counts back from the size of the list *after* it's grown by one:
     :::dart
     var letters = ["a", "b", "c"]
     letters.insert(3, "d")   // OK: inserts at end.
-    IO.print(letters)        // ["a", "b", "c", "d"]
+    System.print(letters)        // ["a", "b", "c", "d"]
     letters.insert(-2, "e")  // Counts back from size after insert.
-    IO.print(letters)        // ["a", "b", "c", "e", "d"]
+    System.print(letters)        // ["a", "b", "c", "e", "d"]
 
 ## Removing elements
 
@@ -97,15 +97,15 @@ gap:
     :::dart
     var letters = ["a", "b", "c", "d"]
     letters.removeAt(1)
-    IO.print(letters) // ["a", "c", "d"]
+    System.print(letters) // ["a", "c", "d"]
 
 The `removeAt` method returns the removed item:
 
     :::dart
-    IO.print(letters.removeAt(1)) // "c"
+    System.print(letters.removeAt(1)) // "c"
 
 If you want to remove everything from the list, you can clear it:
 
     :::dart
     hirsute.clear()
-    IO.print(hirsute) // []
+    System.print(hirsute) // []
diff --git a/doc/site/maps.markdown b/doc/site/maps.markdown
index b3924868..1b79e7c5 100644
--- a/doc/site/maps.markdown
+++ b/doc/site/maps.markdown
@@ -58,7 +58,7 @@ To find the value associated with some key, again you use your friend the
 subscript operator:
 
     :::dart
-    IO.print(capitals["Idaho"]) // "Boise".
+    System.print(capitals["Idaho"]) // "Boise".
 
 If the key is present, this returns its value. Otherwise, it returns `null`. Of
 course, `null` itself can also be used as a value, so seeing `null` here
@@ -69,15 +69,15 @@ To tell definitively if a key exists, you can call `containsKey()`:
     :::dart
     var belief = {"nihilism": null}
 
-    IO.print(belief["nihilism"]) // "null" though key exists.
-    IO.print(belief["solipsism"]) // Also "null".
-    IO.print(belief.containsKey("nihilism")) // "true".
-    IO.print(belief.containsKey("solipsism")) // "false".
+    System.print(belief["nihilism"]) // "null" though key exists.
+    System.print(belief["solipsism"]) // Also "null".
+    System.print(belief.containsKey("nihilism")) // "true".
+    System.print(belief.containsKey("solipsism")) // "false".
 
 You can see how many entries a map contains using `count`:
 
     :::dart
-    IO.print(capitals.count) // "3".
+    System.print(capitals.count) // "3".
 
 ## Removing entries
 
@@ -86,12 +86,12 @@ entry you want to delete:
 
     :::dart
     capitals.remove("Maine")
-    IO.print(capitals.containsKey("Maine")) // "false".
+    System.print(capitals.containsKey("Maine")) // "false".
 
 If the key was found, this returns the value that was associated with it:
 
     :::dart
-    IO.print(capitals.remove("Georgia")) // "Atlanta".
+    System.print(capitals.remove("Georgia")) // "Atlanta".
 
 If the key wasn't in the map to begin with, `remove()` just returns `null`.
 
@@ -100,7 +100,7 @@ can just call `clear()`:
 
     :::dart
     capitals.clear()
-    IO.print(capitals.count) // "0".
+    System.print(capitals.count) // "0".
 
 [lists]: lists.html
 
@@ -120,14 +120,14 @@ If you want to see all of the key-value pairs in a map, the easiest way is to
 iterate over the keys and use each to look up its value:
 
     :::dart
-    var stateBirds = {
+    var birds = {
       "Arizona": "Cactus wren",
       "Hawaii": "Nēnē",
       "Ohio": "Northern Cardinal"
     }
 
-    for (state in stateBirds.keys) {
-      IO.print("The state bird of ", state, " is ", stateBirds[state])
+    for (state in birds.keys) {
+      System.print("The state bird of " + state + " is " + birds[state])
     }
 
 This program will print the three states and their birds. However, the *order*
diff --git a/doc/site/modules.markdown b/doc/site/modules.markdown
index ce18899b..44402398 100644
--- a/doc/site/modules.markdown
+++ b/doc/site/modules.markdown
@@ -173,7 +173,7 @@ like:
     import "shared"
 
     // shared.wren
-    IO.print("Shared!")
+    System.print("Shared!")
 
 Here, "a" and "b" both want to use "shared". If "shared" defines some top-level
 state, we only want a single copy of that in memory. To handle this, a module's
@@ -211,14 +211,14 @@ For example:
     import "a"
 
     // a.wren
-    IO.print("start a")
+    System.print("start a")
     import "b"
-    IO.print("end a")
+    System.print("end a")
 
     // b.wren
-    IO.print("start b")
+    System.print("start b")
     import "a"
-    IO.print("end b")
+    System.print("end b")
 
 This program runs successfully and prints:
 
diff --git a/doc/site/syntax.markdown b/doc/site/syntax.markdown
index 00f0b748..7c891237 100644
--- a/doc/site/syntax.markdown
+++ b/doc/site/syntax.markdown
@@ -54,15 +54,15 @@ Newlines (`\n`) are meaningful in Wren. They are used to separate statements:
 
     :::dart
     // Two statements:
-    IO.print("hi") // Newline.
-    IO.print("bye")
+    System.print("hi") // Newline.
+    System.print("bye")
 
 Sometimes, though, a statement doesn't fit on a single line and jamming a
 newline in the middle would trip it up. To handle that, Wren has a very simple
 rule: It ignores a newline following any token that can't end a statement.
 
     :::dart
-    IO.print( // Newline here is ignored.
+    System.print( // Newline here is ignored.
         "hi")
 
 In practice, this means you can put each statement on its own line and wrap
@@ -79,16 +79,16 @@ statement for the else:
     :::dart
     if (happy && knowIt) {
       hands.clap
-    } else IO.print("sad")
+    } else System.print("sad")
 
 Blocks have two similar but not identical forms. Typically, blocks contain a
 series of statements like:
 
     :::dart
     {
-      IO.print("one")
-      IO.print("two")
-      IO.print("three")
+      System.print("one")
+      System.print("two")
+      System.print("three")
     }
 
 Blocks of this form when used for method and function bodies automatically
diff --git a/doc/site/template-core.html b/doc/site/template-core.html
index 0476d5b1..31d8d958 100644
--- a/doc/site/template-core.html
+++ b/doc/site/template-core.html
@@ -38,7 +38,7 @@
         <li><a href="range.html">Range</a></li>
         <li><a href="sequence.html">Sequence</a></li>
         <li><a href="string.html">String</a></li>
-        <li><a href="io.html">IO</a></li>
+        <li><a href="system.html">System</a></li>
       </ul>
     </section>
   </nav>
diff --git a/doc/site/values.markdown b/doc/site/values.markdown
index a50c01c8..14855239 100644
--- a/doc/site/values.markdown
+++ b/doc/site/values.markdown
@@ -57,11 +57,11 @@ A handful of escape characters are supported:
 A `\u` followed by four hex digits can be used to specify a Unicode code point:
 
     :::dart
-    IO.print("\u0041\u0b83\u00DE") // "AஃÞ"
+    System.print("\u0041\u0b83\u00DE") // "AஃÞ"
 
 A `\x` followed by two hex digits specifies a single unencoded byte:
 
-    IO.print("\x48\x69\x2e") // "Hi."
+    System.print("\x48\x69\x2e") // "Hi."
 
 Strings are instances of class [String](core/string.html).
 
@@ -90,7 +90,7 @@ example:
     :::dart
     var list = ["a", "b", "c", "d", "e"]
     var slice = list[1..3]
-    IO.print(slice) // ["b", "c", "d"]
+    System.print(slice) // ["b", "c", "d"]
 
 Their class is [Range](core/range.html).
 
diff --git a/doc/site/variables.markdown b/doc/site/variables.markdown
index 1cd1d4d9..e1ee5020 100644
--- a/doc/site/variables.markdown
+++ b/doc/site/variables.markdown
@@ -13,7 +13,7 @@ defined, it can be accessed by name as you would expect.
 
     :::dart
     var animal = "Slow Loris"
-    IO.print(animal) // Prints "Slow Loris".
+    System.print(animal) // Prints "Slow Loris".
 
 ## Scope
 
@@ -22,11 +22,11 @@ until the end of the [block](syntax.html#blocks) where that definition appears.
 
     :::dart
     {
-      IO.print(a) // ERROR! a doesn't exist yet.
+      System.print(a) // ERROR! a doesn't exist yet.
       var a = 123
-      IO.print(a) // "123"
+      System.print(a) // "123"
     }
-    IO.print(a) // ERROR! a doesn't exist anymore.
+    System.print(a) // ERROR! a doesn't exist anymore.
 
 Variables defined at the top level of a script are *top-level* and are visible
 to the [module](modules.html) system. All other variables are *local*.
@@ -38,9 +38,9 @@ intend to do much).
     var a = "outer"
     {
       var a = "inner"
-      IO.print(a) // Prints "inner".
+      System.print(a) // Prints "inner".
     }
-    IO.print(a) // Prints "outer".
+    System.print(a) // Prints "outer".
 
 Declaring a variable with the same name in the *same* scope *is* an error.
 
@@ -65,6 +65,6 @@ assigned value.
 
     :::dart
     var a = "before"
-    IO.print(a = "after") // Prints "after".
+    System.print(a = "after") // Prints "after".
 
 **TODO: Top-level names.**
diff --git a/example/hello.wren b/example/hello.wren
index 0bb440c3..3cfadf03 100644
--- a/example/hello.wren
+++ b/example/hello.wren
@@ -1 +1 @@
-IO.print("Hello, world!")
+System.print("Hello, world!")
diff --git a/example/import-module/lovecraft.wren b/example/import-module/lovecraft.wren
index 728c081a..57b11331 100644
--- a/example/import-module/lovecraft.wren
+++ b/example/import-module/lovecraft.wren
@@ -5,4 +5,4 @@ class Lovecraft {
   say() { Cthulu.new().message }
 }
 
-IO.print(Lovecraft.new().say())
+System.print(Lovecraft.new().say())
diff --git a/example/mandelbrot.wren b/example/mandelbrot.wren
index 31bc86c0..89cf5a17 100644
--- a/example/mandelbrot.wren
+++ b/example/mandelbrot.wren
@@ -29,8 +29,8 @@ for (yPixel in 0...24) {
       }
     }
 
-    IO.write(pixel)
+    System.write(pixel)
   }
 
-  IO.print("")
-}
\ No newline at end of file
+  System.print()
+}
diff --git a/example/sokoban.wren b/example/sokoban.wren
deleted file mode 100644
index 0bb440c3..00000000
--- a/example/sokoban.wren
+++ /dev/null
@@ -1 +0,0 @@
-IO.print("Hello, world!")
diff --git a/example/syntax.wren b/example/syntax.wren
index affd4462..52d440f5 100644
--- a/example/syntax.wren
+++ b/example/syntax.wren
@@ -9,7 +9,7 @@ class SyntaxExample {
   // Constructor
   construct new() {
     // Top-level name `IO`
-    IO.print("I am a constructor!")
+    System.print("I am a constructor!")
 
     // Method calls
     variables
@@ -58,7 +58,7 @@ class SyntaxExample {
   field=(value) { _field = value }
 
   // Method with arguments
-  print(a, b) { IO.print(a + b) }
+  print(a, b) { System.print(a + b) }
 
   // Operators
   +(other) { "infix + " + other }
@@ -97,7 +97,7 @@ class ReservedWords is SyntaxExample {
 
     // `for`, `in`
     for (beatle in ["george", "john", "paul", "ringo"]) {
-      IO.print(beatle)
+      System.print(beatle)
       // `break`
       break
     }
@@ -147,9 +147,9 @@ class Literals is SyntaxExample {
     "\t" // Tab.
     "\v" // Vertical tab.
     // Unicode code points
-    IO.print("\u0041fgdg\u0b83\u00DE") // "AஃÞ"
+    System.print("\u0041fgdg\u0b83\u00DE") // "AஃÞ"
     // Unencoded bytes
-    IO.print("\x48\x69\x2e") // "Hi."
+    System.print("\x48\x69\x2e") // "Hi."
   }
 
   ranges {
diff --git a/project/xcode/wren.xcodeproj/project.pbxproj b/project/xcode/wren.xcodeproj/project.pbxproj
index 5e493348..678282b8 100644
--- a/project/xcode/wren.xcodeproj/project.pbxproj
+++ b/project/xcode/wren.xcodeproj/project.pbxproj
@@ -17,7 +17,6 @@
 		29205C991AB4E6430073018D /* wren_compiler.c in Sources */ = {isa = PBXBuildFile; fileRef = 29205C921AB4E6430073018D /* wren_compiler.c */; };
 		29205C9A1AB4E6430073018D /* wren_core.c in Sources */ = {isa = PBXBuildFile; fileRef = 29205C931AB4E6430073018D /* wren_core.c */; };
 		29205C9B1AB4E6430073018D /* wren_debug.c in Sources */ = {isa = PBXBuildFile; fileRef = 29205C941AB4E6430073018D /* wren_debug.c */; };
-		29205C9C1AB4E6430073018D /* wren_io.c in Sources */ = {isa = PBXBuildFile; fileRef = 29205C951AB4E6430073018D /* wren_io.c */; };
 		29205C9D1AB4E6430073018D /* wren_utils.c in Sources */ = {isa = PBXBuildFile; fileRef = 29205C961AB4E6430073018D /* wren_utils.c */; };
 		29205C9E1AB4E6430073018D /* wren_value.c in Sources */ = {isa = PBXBuildFile; fileRef = 29205C971AB4E6430073018D /* wren_value.c */; };
 		29205C9F1AB4E6430073018D /* wren_vm.c in Sources */ = {isa = PBXBuildFile; fileRef = 29205C981AB4E6430073018D /* wren_vm.c */; };
@@ -63,7 +62,6 @@
 		29205C921AB4E6430073018D /* wren_compiler.c */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.c; name = wren_compiler.c; path = ../../src/vm/wren_compiler.c; sourceTree = "<group>"; };
 		29205C931AB4E6430073018D /* wren_core.c */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.c; name = wren_core.c; path = ../../src/vm/wren_core.c; sourceTree = "<group>"; };
 		29205C941AB4E6430073018D /* wren_debug.c */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.c; name = wren_debug.c; path = ../../src/vm/wren_debug.c; sourceTree = "<group>"; };
-		29205C951AB4E6430073018D /* wren_io.c */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.c; name = wren_io.c; path = ../../src/vm/wren_io.c; sourceTree = "<group>"; };
 		29205C961AB4E6430073018D /* wren_utils.c */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.c; name = wren_utils.c; path = ../../src/vm/wren_utils.c; sourceTree = "<group>"; };
 		29205C971AB4E6430073018D /* wren_value.c */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.c; name = wren_value.c; path = ../../src/vm/wren_value.c; sourceTree = "<group>"; };
 		29205C981AB4E6430073018D /* wren_vm.c */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.c; name = wren_vm.c; path = ../../src/vm/wren_vm.c; sourceTree = "<group>"; };
@@ -71,7 +69,6 @@
 		29205CA21AB4E65E0073018D /* wren_compiler.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = wren_compiler.h; path = ../../src/vm/wren_compiler.h; sourceTree = "<group>"; };
 		29205CA31AB4E65E0073018D /* wren_core.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = wren_core.h; path = ../../src/vm/wren_core.h; sourceTree = "<group>"; };
 		29205CA41AB4E65E0073018D /* wren_debug.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = wren_debug.h; path = ../../src/vm/wren_debug.h; sourceTree = "<group>"; };
-		29205CA51AB4E65E0073018D /* wren_io.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = wren_io.h; path = ../../src/vm/wren_io.h; sourceTree = "<group>"; };
 		29205CA61AB4E65E0073018D /* wren_utils.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = wren_utils.h; path = ../../src/vm/wren_utils.h; sourceTree = "<group>"; };
 		29205CA71AB4E65E0073018D /* wren_value.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = wren_value.h; path = ../../src/vm/wren_value.h; sourceTree = "<group>"; };
 		29205CA81AB4E65E0073018D /* wren_vm.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; name = wren_vm.h; path = ../../src/vm/wren_vm.h; sourceTree = "<group>"; };
@@ -137,8 +134,6 @@
 				29205C931AB4E6430073018D /* wren_core.c */,
 				29205CA41AB4E65E0073018D /* wren_debug.h */,
 				29205C941AB4E6430073018D /* wren_debug.c */,
-				29205CA51AB4E65E0073018D /* wren_io.h */,
-				29205C951AB4E6430073018D /* wren_io.c */,
 				29DE39521AC3A50A00987D41 /* wren_meta.h */,
 				29DE39511AC3A50A00987D41 /* wren_meta.c */,
 				296371B31AC713D000079FDA /* wren_opcodes.h */,
@@ -292,7 +287,6 @@
 				29C8A9331AB71FFF00DEC81D /* vm.c in Sources */,
 				291647C41BA5EA45006142EE /* scheduler.c in Sources */,
 				29205C9B1AB4E6430073018D /* wren_debug.c in Sources */,
-				29205C9C1AB4E6430073018D /* wren_io.c in Sources */,
 				29205C9D1AB4E6430073018D /* wren_utils.c in Sources */,
 				29205C9E1AB4E6430073018D /* wren_value.c in Sources */,
 				29205C9F1AB4E6430073018D /* wren_vm.c in Sources */,
diff --git a/script/test.py b/script/test.py
index 4c44bfdf..9b922c6c 100755
--- a/script/test.py
+++ b/script/test.py
@@ -14,7 +14,7 @@ WREN_DIR = dirname(dirname(realpath(__file__)))
 WREN_APP = join(WREN_DIR, 'bin', 'wrend')
 TEST_APP = join(WREN_DIR, 'build', 'debug', 'test', 'wrend')
 
-EXPECT_PATTERN = re.compile(r'// expect: (.*)')
+EXPECT_PATTERN = re.compile(r'// expect: ?(.*)')
 EXPECT_ERROR_PATTERN = re.compile(r'// expect error(?! line)')
 EXPECT_ERROR_LINE_PATTERN = re.compile(r'// expect error line (\d+)')
 EXPECT_RUNTIME_ERROR_PATTERN = re.compile(r'// expect runtime error: (.+)')
diff --git a/src/vm/wren_common.h b/src/vm/wren_common.h
index 834f7eb8..491a8ad1 100644
--- a/src/vm/wren_common.h
+++ b/src/vm/wren_common.h
@@ -44,13 +44,6 @@
   #endif
 #endif
 
-// If true, loads the "IO" class in the standard library.
-//
-// Defaults to on.
-#ifndef WREN_USE_LIB_IO
-  #define WREN_USE_LIB_IO 1
-#endif
-
 // If true, loads the "Meta" class in the standard library.
 //
 // Defaults to on.
diff --git a/src/vm/wren_core.c b/src/vm/wren_core.c
index 3bd48e24..55503075 100644
--- a/src/vm/wren_core.c
+++ b/src/vm/wren_core.c
@@ -4,6 +4,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 
 #include "wren_common.h"
 #include "wren_core.h"
@@ -1041,6 +1042,17 @@ DEF_PRIMITIVE(string_toString)
   RETURN_VAL(args[0]);
 }
 
+DEF_PRIMITIVE(system_clock)
+{
+  RETURN_NUM((double)clock() / CLOCKS_PER_SEC);
+}
+
+DEF_PRIMITIVE(system_writeString)
+{
+  printf("%s", AS_CSTRING(args[1]));
+  RETURN_VAL(args[1]);
+}
+
 // Creates either the Object or Class class in the core library with [name].
 static ObjClass* defineClass(WrenVM* vm, ObjModule* module, const char* name)
 {
@@ -1254,6 +1266,10 @@ void wrenInitializeCore(WrenVM* vm)
   PRIMITIVE(vm->rangeClass, "iteratorValue(_)", range_iteratorValue);
   PRIMITIVE(vm->rangeClass, "toString", range_toString);
 
+  ObjClass* systemClass = AS_CLASS(wrenFindVariable(vm, coreModule, "System"));
+  PRIMITIVE(systemClass->obj.classObj, "clock", system_clock);
+  PRIMITIVE(systemClass->obj.classObj, "writeString_(_)", system_writeString);
+  
   // While bootstrapping the core types and running the core library, a number
   // of string objects have been created, many of which were instantiated
   // before stringClass was stored in the VM. Some of them *must* be created
diff --git a/src/vm/wren_core.wren.inc b/src/vm/wren_core.wren.inc
index 96ff3a16..e9c42ffa 100644
--- a/src/vm/wren_core.wren.inc
+++ b/src/vm/wren_core.wren.inc
@@ -214,4 +214,39 @@ static const char* coreModuleSource =
 "  iteratorValue(iterator) { _map.valueIteratorValue_(iterator) }\n"
 "}\n"
 "\n"
-"class Range is Sequence {}\n";
+"class Range is Sequence {}\n"
+"\n"
+"class System {\n"
+"  static print() {\n"
+"    writeString_(\"\n\")\n"
+"  }\n"
+"\n"
+"  static print(obj) {\n"
+"    writeObject_(obj)\n"
+"    writeString_(\"\n\")\n"
+"    return obj\n"
+"  }\n"
+"\n"
+"  static printAll(sequence) {\n"
+"    for (object in sequence) writeObject_(object)\n"
+"    writeString_(\"\n\")\n"
+"  }\n"
+"\n"
+"  static write(obj) {\n"
+"    writeObject_(obj)\n"
+"    return obj\n"
+"  }\n"
+"\n"
+"  static writeAll(sequence) {\n"
+"    for (object in sequence) writeObject_(object)\n"
+"  }\n"
+"\n"
+"  static writeObject_(obj) {\n"
+"    var string = obj.toString\n"
+"    if (string is String) {\n"
+"      writeString_(string)\n"
+"    } else {\n"
+"      writeString_(\"[invalid toString]\")\n"
+"    }\n"
+"  }\n"
+"}\n";
diff --git a/src/vm/wren_io.c b/src/vm/wren_io.c
deleted file mode 100644
index 1b0201fd..00000000
--- a/src/vm/wren_io.c
+++ /dev/null
@@ -1,59 +0,0 @@
-#include "wren_io.h"
-
-#if WREN_USE_LIB_IO
-
-#include <stdio.h>
-#include <string.h>
-#include <time.h>
-
-// TODO: This is an arbitrary limit. Do something smarter.
-#define MAX_READ_LEN 1024
-
-#include "wren_io.wren.inc"
-
-static void ioWriteString(WrenVM* vm)
-{
-  const char* s = wrenGetArgumentString(vm, 1);
-  // TODO: Check for null.
-  printf("%s", s);
-}
-
-static void ioRead(WrenVM* vm)
-{
-  char buffer[MAX_READ_LEN];
-  char* result = fgets(buffer, MAX_READ_LEN, stdin);
-
-  if (result != NULL)
-  {
-    wrenReturnString(vm, buffer, (int)strlen(buffer));
-  }
-}
-
-static void ioClock(WrenVM* vm)
-{
-  wrenReturnDouble(vm, (double)clock() / CLOCKS_PER_SEC);
-}
-
-static void ioTime(WrenVM* vm)
-{
-  wrenReturnDouble(vm, (double)time(NULL));
-}
-
-void wrenLoadIOLibrary(WrenVM* vm)
-{
-  wrenInterpret(vm, "", ioModuleSource);
-}
-
-WrenForeignMethodFn wrenBindIOForeignMethod(WrenVM* vm, const char* className,
-                                            const char* signature)
-{
-  if (strcmp(className, "IO") != 0) return NULL;
-
-  if (strcmp(signature, "writeString_(_)") == 0) return ioWriteString;
-  if (strcmp(signature, "clock") == 0) return ioClock;
-  if (strcmp(signature, "time") == 0) return ioTime;
-  if (strcmp(signature, "read()") == 0) return ioRead;
-  return NULL;
-}
-
-#endif
diff --git a/src/vm/wren_io.h b/src/vm/wren_io.h
deleted file mode 100644
index 4c052b64..00000000
--- a/src/vm/wren_io.h
+++ /dev/null
@@ -1,18 +0,0 @@
-#ifndef wren_io_h
-#define wren_io_h
-
-#include "wren.h"
-#include "wren_common.h"
-
-// This module defines the IO class and its associated methods. They are
-// implemented using the C standard library.
-#if WREN_USE_LIB_IO
-
-void wrenLoadIOLibrary(WrenVM* vm);
-
-WrenForeignMethodFn wrenBindIOForeignMethod(WrenVM* vm, const char* className,
-                                            const char* signature);
-
-#endif
-
-#endif
diff --git a/src/vm/wren_io.wren.inc b/src/vm/wren_io.wren.inc
deleted file mode 100644
index d9ced63d..00000000
--- a/src/vm/wren_io.wren.inc
+++ /dev/null
@@ -1,103 +0,0 @@
-// Generated automatically from builtin/io.wren. Do not edit.
-static const char* ioModuleSource =
-"class IO {\n"
-"  static print {\n"
-"    writeString_(\"\n\")\n"
-"  }\n"
-"\n"
-"  static print(obj) {\n"
-"    writeObject_(obj)\n"
-"    writeString_(\"\n\")\n"
-"    return obj\n"
-"  }\n"
-"\n"
-"  static print(a1, a2) {\n"
-"    printAll([a1, a2])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3) {\n"
-"    printAll([a1, a2, a3])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4) {\n"
-"    printAll([a1, a2, a3, a4])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5) {\n"
-"    printAll([a1, a2, a3, a4, a5])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6, a7) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6, a7])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6, a7, a8) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6, a7, a8])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15])\n"
-"  }\n"
-"\n"
-"  static print(a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16) {\n"
-"    printAll([a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16])\n"
-"  }\n"
-"\n"
-"  static printAll(sequence) {\n"
-"    for (object in sequence) writeObject_(object)\n"
-"    writeString_(\"\n\")\n"
-"  }\n"
-"\n"
-"  static write(obj) {\n"
-"    writeObject_(obj)\n"
-"    return obj\n"
-"  }\n"
-"\n"
-"  static read(prompt) {\n"
-"    if (!(prompt is String)) Fiber.abort(\"Prompt must be a string.\")\n"
-"    write(prompt)\n"
-"    return read()\n"
-"  }\n"
-"\n"
-"  static writeObject_(obj) {\n"
-"    var string = obj.toString\n"
-"    if (string is String) {\n"
-"      writeString_(string)\n"
-"    } else {\n"
-"      writeString_(\"[invalid toString]\")\n"
-"    }\n"
-"  }\n"
-"\n"
-"  foreign static writeString_(string)\n"
-"  foreign static clock\n"
-"  foreign static time\n"
-"  foreign static read()\n"
-"}\n";
diff --git a/src/vm/wren_vm.c b/src/vm/wren_vm.c
index 6aefa3ee..717050a2 100644
--- a/src/vm/wren_vm.c
+++ b/src/vm/wren_vm.c
@@ -298,20 +298,6 @@ static WrenForeignMethodFn findForeignMethod(WrenVM* vm,
                                              bool isStatic,
                                              const char* signature)
 {
-  WrenForeignMethodFn fn;
-
-  // Bind foreign methods in the core module.
-  if (strcmp(moduleName, "core") == 0)
-  {
-    #if WREN_USE_LIB_IO
-    fn = wrenBindIOForeignMethod(vm, className, signature);
-    #endif
-    
-    ASSERT(fn != NULL, "Failed to bind core module foreign method.");
-    return fn;
-  }
-
-  // For other modules, let the host bind it.
   if (vm->bindForeignMethod == NULL) return NULL;
 
   return vm->bindForeignMethod(vm, moduleName, className, isStatic, signature);
diff --git a/test/README.md b/test/README.md
index 9652fa8e..bb090509 100644
--- a/test/README.md
+++ b/test/README.md
@@ -8,9 +8,6 @@ This contains the automated validation suite for the VM and built-in libraries.
   classes. If a bug is in `wren_core.c` or `wren_value.c`, it will most likely
   break one of these tests.
 
-* `io/` - Tests for the built in IO library. In other words, methods on the
-  `IO` class. If a bug is in `wren_io.c`, it should break one of these tests.
-
 * `language/` - Tests of the language itself, its grammar and runtime
   semantics. If a bug is in `wren_compiler.c` or `wren_vm.c`, it will most
   likely break one of these tests. This includes tests for the syntax for the
diff --git a/test/api/foreign_class.wren b/test/api/foreign_class.wren
index 03889f4d..b3affda0 100644
--- a/test/api/foreign_class.wren
+++ b/test/api/foreign_class.wren
@@ -11,27 +11,27 @@ foreign class Counter {
 }
 
 var counter = Counter.new()
-IO.print(counter.value) // expect: 0
+System.print(counter.value) // expect: 0
 counter.increment(3.1)
-IO.print(counter.value) // expect: 3.1
+System.print(counter.value) // expect: 3.1
 counter.increment(1.2)
-IO.print(counter.value) // expect: 4.3
+System.print(counter.value) // expect: 4.3
 
 // Foreign classes can inherit a class as long as it has no fields.
 class PointBase {
   inherited() {
-    IO.print("inherited method")
+    System.print("inherited method")
   }
 }
 
 // Class with non-default constructor.
 foreign class Point is PointBase {
   construct new() {
-    IO.print("default")
+    System.print("default")
   }
 
   construct new(x, y, z) {
-    IO.print(x, ", ", y, ", ", z)
+    System.print(x.toString + ", " + y.toString + ", " + z.toString)
   }
 
   foreign translate(x, y, z)
@@ -39,19 +39,19 @@ foreign class Point is PointBase {
 }
 
 var p = Point.new(1, 2, 3) // expect: 1, 2, 3
-IO.print(p) // expect: (1, 2, 3)
+System.print(p) // expect: (1, 2, 3)
 p.translate(3, 4, 5)
-IO.print(p) // expect: (4, 6, 8)
+System.print(p) // expect: (4, 6, 8)
 
 p = Point.new() // expect: default
-IO.print(p) // expect: (0, 0, 0)
+System.print(p) // expect: (0, 0, 0)
 
 p.inherited() // expect: inherited method
 
 var error = Fiber.new {
   class Subclass is Point {}
 }.try()
-IO.print(error) // expect: Class 'Subclass' cannot inherit from foreign class 'Point'.
+System.print(error) // expect: Class 'Subclass' cannot inherit from foreign class 'Point'.
 
 // Class with a finalizer.
 foreign class Resource {
@@ -65,14 +65,14 @@ var resources = [
 ]
 
 Api.gc()
-IO.print(Api.finalized) // expect: 0
+System.print(Api.finalized) // expect: 0
 
 resources.removeAt(-1)
 
 Api.gc()
-IO.print(Api.finalized) // expect: 1
+System.print(Api.finalized) // expect: 1
 
 resources.clear()
 
 Api.gc()
-IO.print(Api.finalized) // expect: 3
+System.print(Api.finalized) // expect: 3
diff --git a/test/api/returns.wren b/test/api/returns.wren
index f607eef6..dade69ec 100644
--- a/test/api/returns.wren
+++ b/test/api/returns.wren
@@ -8,10 +8,10 @@ class Api {
   foreign static returnFalse
 }
 
-IO.print(Api.implicitNull == null) // expect: true
+System.print(Api.implicitNull == null) // expect: true
 
-IO.print(Api.returnInt)  // expect: 123456
-IO.print(Api.returnFloat) // expect: 123.456
+System.print(Api.returnInt)  // expect: 123456
+System.print(Api.returnFloat) // expect: 123.456
 
-IO.print(Api.returnTrue)  // expect: true
-IO.print(Api.returnFalse) // expect: false
+System.print(Api.returnTrue)  // expect: true
+System.print(Api.returnFalse) // expect: false
diff --git a/test/api/value.wren b/test/api/value.wren
index e3e07d4f..c348869f 100644
--- a/test/api/value.wren
+++ b/test/api/value.wren
@@ -11,4 +11,4 @@ for (i in 1...10) {
   s = s + " more"
 }
 
-IO.print(Api.value) // expect: [list, of, strings]
+System.print(Api.value) // expect: [list, of, strings]
diff --git a/test/benchmark/binary_trees.wren b/test/benchmark/binary_trees.wren
index 3bf44d03..05028c06 100644
--- a/test/benchmark/binary_trees.wren
+++ b/test/benchmark/binary_trees.wren
@@ -24,10 +24,10 @@ var minDepth = 4
 var maxDepth = 12
 var stretchDepth = maxDepth + 1
 
-var start = IO.clock
+var start = System.clock
 
-IO.print("stretch tree of depth ", stretchDepth, " check: ",
-    Tree.new(0, stretchDepth).check)
+System.print("stretch tree of depth " + stretchDepth.toString + " check: " +
+    Tree.new(0, stretchDepth).check.toString)
 
 var longLivedTree = Tree.new(0, maxDepth)
 
@@ -44,10 +44,12 @@ while (depth < stretchDepth) {
     check = check + Tree.new(i, depth).check + Tree.new(-i, depth).check
   }
 
-  IO.print((iterations * 2), " trees of depth ", depth, " check: ", check)
+  System.print((iterations * 2).toString + " trees of depth " +
+      depth.toString + " check: " + check.toString)
   iterations = iterations / 4
   depth = depth + 2
 }
 
-IO.print("long lived tree of depth ", maxDepth, " check: ", longLivedTree.check)
-IO.print("elapsed: ", (IO.clock - start))
+System.print("long lived tree of depth " + maxDepth.toString + " check: " +
+    longLivedTree.check.toString)
+System.print("elapsed: " + (System.clock - start).toString)
diff --git a/test/benchmark/delta_blue.wren b/test/benchmark/delta_blue.wren
index 74fafafd..8311bf0a 100644
--- a/test/benchmark/delta_blue.wren
+++ b/test/benchmark/delta_blue.wren
@@ -92,7 +92,7 @@ class Constraint {
     chooseMethod(mark)
     if (!isSatisfied) {
       if (_strength == REQUIRED) {
-        IO.print("Could not satisfy a required constraint!")
+        System.print("Could not satisfy a required constraint!")
       }
       return null
     }
@@ -102,7 +102,7 @@ class Constraint {
     var overridden = out.determinedBy
     if (overridden != null) overridden.markUnsatisfied
     out.determinedBy = this
-    if (!ThePlanner.addPropagate(this, mark)) IO.print("Cycle encountered")
+    if (!ThePlanner.addPropagate(this, mark)) System.print("Cycle encountered")
     out.mark = mark
     return overridden
   }
@@ -669,31 +669,31 @@ var projectionTest = Fn.new {|n|
 
   change.call(src, 17)
   total = total + dst.value
-  if (dst.value != 1170) IO.print("Projection 1 failed")
+  if (dst.value != 1170) System.print("Projection 1 failed")
 
   change.call(dst, 1050)
 
   total = total + src.value
-  if (src.value != 5) IO.print("Projection 2 failed")
+  if (src.value != 5) System.print("Projection 2 failed")
 
   change.call(scale, 5)
   for (i in 0...n - 1) {
     total = total + dests[i].value
-    if (dests[i].value != i * 5 + 1000) IO.print("Projection 3 failed")
+    if (dests[i].value != i * 5 + 1000) System.print("Projection 3 failed")
   }
 
   change.call(offset, 2000)
   for (i in 0...n - 1) {
     total = total + dests[i].value
-    if (dests[i].value != i * 5 + 2000) IO.print("Projection 4 failed")
+    if (dests[i].value != i * 5 + 2000) System.print("Projection 4 failed")
   }
 }
 
-var start = IO.clock
+var start = System.clock
 for (i in 0...40) {
   chainTest.call(100)
   projectionTest.call(100)
 }
 
-IO.print(total)
-IO.print("elapsed: ", IO.clock - start)
+System.print(total)
+System.print("elapsed: " + (System.clock - start).toString)
diff --git a/test/benchmark/fib.wren b/test/benchmark/fib.wren
index 35c89dfb..dcad88f0 100644
--- a/test/benchmark/fib.wren
+++ b/test/benchmark/fib.wren
@@ -5,8 +5,8 @@ class Fib {
   }
 }
 
-var start = IO.clock
+var start = System.clock
 for (i in 1..5) {
-  IO.print(Fib.get(28))
+  System.print(Fib.get(28))
 }
-IO.print("elapsed: ", IO.clock - start)
+System.print("elapsed: " + (System.clock - start).toString)
diff --git a/test/benchmark/fibers.wren b/test/benchmark/fibers.wren
index 83ff0f79..a30da99c 100644
--- a/test/benchmark/fibers.wren
+++ b/test/benchmark/fibers.wren
@@ -2,7 +2,7 @@
 var fibers = []
 var sum = 0
 
-var start = IO.clock
+var start = System.clock
 
 for (i in 0...100000) {
   fibers.add(Fiber.new {
@@ -12,5 +12,5 @@ for (i in 0...100000) {
 }
 
 fibers[0].call()
-IO.print(sum)
-IO.print("elapsed: ", IO.clock - start)
+System.print(sum)
+System.print("elapsed: " + (System.clock - start).toString)
diff --git a/test/benchmark/for.wren b/test/benchmark/for.wren
index f76d0041..1546c909 100644
--- a/test/benchmark/for.wren
+++ b/test/benchmark/for.wren
@@ -1,10 +1,10 @@
 var list = []
 
-var start = IO.clock
+var start = System.clock
 for (i in 0...1000000) list.add(i)
 
 var sum = 0
 for (i in list) sum = sum + i
 
-IO.print(sum)
-IO.print("elapsed: ", IO.clock - start)
+System.print(sum)
+System.print("elapsed: " + (System.clock - start).toString)
diff --git a/test/benchmark/map_numeric.wren b/test/benchmark/map_numeric.wren
index b07b5fe2..e6b226a6 100644
--- a/test/benchmark/map_numeric.wren
+++ b/test/benchmark/map_numeric.wren
@@ -1,4 +1,4 @@
-var start = IO.clock
+var start = System.clock
 
 var map = {}
 
@@ -10,10 +10,10 @@ var sum = 0
 for (i in 1..1000000) {
   sum = sum + map[i]
 }
-IO.print(sum)
+System.print(sum)
 
 for (i in 1..1000000) {
   map.remove(i)
 }
 
-IO.print("elapsed: ", IO.clock - start)
+System.print("elapsed: " + (System.clock - start).toString)
diff --git a/test/benchmark/map_string.wren b/test/benchmark/map_string.wren
index f0157bf9..b31a4137 100644
--- a/test/benchmark/map_string.wren
+++ b/test/benchmark/map_string.wren
@@ -77,7 +77,7 @@ for (animal in animals) {
   }
 }
 
-var start = IO.clock
+var start = System.clock
 
 var map = {}
 
@@ -96,5 +96,5 @@ for (key in keys) {
   map.remove(key)
 }
 
-IO.print(sum)
-IO.print("elapsed: ", IO.clock - start)
+System.print(sum)
+System.print("elapsed: " + (System.clock - start).toString)
diff --git a/test/benchmark/method_call.wren b/test/benchmark/method_call.wren
index 71579357..22739e41 100644
--- a/test/benchmark/method_call.wren
+++ b/test/benchmark/method_call.wren
@@ -28,7 +28,7 @@ class NthToggle is Toggle {
   }
 }
 
-var start = IO.clock
+var start = System.clock
 var n = 100000
 var val = true
 var toggle = Toggle.new(val)
@@ -46,7 +46,7 @@ for (i in 0...n) {
   val = toggle.activate.value
 }
 
-IO.print(toggle.value)
+System.print(toggle.value)
 
 val = true
 var ntoggle = NthToggle.new(val, 3)
@@ -64,5 +64,5 @@ for (i in 0...n) {
   val = ntoggle.activate.value
 }
 
-IO.print(ntoggle.value)
-IO.print("elapsed: ", IO.clock - start)
+System.print(ntoggle.value)
+System.print("elapsed: " + (System.clock - start).toString)
diff --git a/test/benchmark/string_equals.wren b/test/benchmark/string_equals.wren
index 52aea3db..6d95af3e 100644
--- a/test/benchmark/string_equals.wren
+++ b/test/benchmark/string_equals.wren
@@ -1,4 +1,4 @@
-var start = IO.clock
+var start = System.clock
 
 var count = 0
 for (i in 1..1000000) {
@@ -20,5 +20,5 @@ for (i in 1..1000000) {
       "another") count = count + 1
 }
 
-IO.print(count)
-IO.print("elapsed: ", IO.clock - start)
+System.print(count)
+System.print("elapsed: " + (System.clock - start).toString)
diff --git a/test/core/bool/equality.wren b/test/core/bool/equality.wren
index 6797482a..1a88261f 100644
--- a/test/core/bool/equality.wren
+++ b/test/core/bool/equality.wren
@@ -1,23 +1,23 @@
-IO.print(true == true)    // expect: true
-IO.print(true == false)   // expect: false
-IO.print(false == true)   // expect: false
-IO.print(false == false)  // expect: true
+System.print(true == true)    // expect: true
+System.print(true == false)   // expect: false
+System.print(false == true)   // expect: false
+System.print(false == false)  // expect: true
 
 // Not equal to other types.
-IO.print(true == 1)        // expect: false
-IO.print(false == 0)       // expect: false
-IO.print(true == "true")   // expect: false
-IO.print(false == "false") // expect: false
-IO.print(false == "")      // expect: false
+System.print(true == 1)        // expect: false
+System.print(false == 0)       // expect: false
+System.print(true == "true")   // expect: false
+System.print(false == "false") // expect: false
+System.print(false == "")      // expect: false
 
-IO.print(true != true)    // expect: false
-IO.print(true != false)   // expect: true
-IO.print(false != true)   // expect: true
-IO.print(false != false)  // expect: false
+System.print(true != true)    // expect: false
+System.print(true != false)   // expect: true
+System.print(false != true)   // expect: true
+System.print(false != false)  // expect: false
 
 // Not equal to other types.
-IO.print(true != 1)        // expect: true
-IO.print(false != 0)       // expect: true
-IO.print(true != "true")   // expect: true
-IO.print(false != "false") // expect: true
-IO.print(false != "")      // expect: true
+System.print(true != 1)        // expect: true
+System.print(false != 0)       // expect: true
+System.print(true != "true")   // expect: true
+System.print(false != "false") // expect: true
+System.print(false != "")      // expect: true
diff --git a/test/core/bool/not.wren b/test/core/bool/not.wren
index cc8b7558..e5d57e34 100644
--- a/test/core/bool/not.wren
+++ b/test/core/bool/not.wren
@@ -1,3 +1,3 @@
-IO.print(!true)    // expect: false
-IO.print(!false)   // expect: true
-IO.print(!!true)   // expect: true
+System.print(!true)    // expect: false
+System.print(!false)   // expect: true
+System.print(!!true)   // expect: true
diff --git a/test/core/bool/to_string.wren b/test/core/bool/to_string.wren
index e23c13c6..85eeb45a 100644
--- a/test/core/bool/to_string.wren
+++ b/test/core/bool/to_string.wren
@@ -1,2 +1,2 @@
-IO.print(true.toString)  // expect: true
-IO.print(false.toString) // expect: false
+System.print(true.toString)  // expect: true
+System.print(false.toString) // expect: false
diff --git a/test/core/bool/type.wren b/test/core/bool/type.wren
index 242b7871..b7c7d38c 100644
--- a/test/core/bool/type.wren
+++ b/test/core/bool/type.wren
@@ -1,4 +1,4 @@
-IO.print(true is Bool)      // expect: true
-IO.print(true is Object)    // expect: true
-IO.print(true is Num)       // expect: false
-IO.print(true.type == Bool) // expect: true
+System.print(true is Bool)      // expect: true
+System.print(true is Object)    // expect: true
+System.print(true is Num)       // expect: false
+System.print(true.type == Bool) // expect: true
diff --git a/test/core/class/equality.wren b/test/core/class/equality.wren
index 51dce1a7..82b36afc 100644
--- a/test/core/class/equality.wren
+++ b/test/core/class/equality.wren
@@ -1,13 +1,13 @@
-IO.print(Num == Num)  // expect: true
-IO.print(Num == Bool) // expect: false
+System.print(Num == Num)  // expect: true
+System.print(Num == Bool) // expect: false
 
 // Not equal to other types.
-IO.print(Num == 123)  // expect: false
-IO.print(Num == true) // expect: false
+System.print(Num == 123)  // expect: false
+System.print(Num == true) // expect: false
 
-IO.print(Num != Num)  // expect: false
-IO.print(Num != Bool) // expect: true
+System.print(Num != Num)  // expect: false
+System.print(Num != Bool) // expect: true
 
 // Not equal to other types.
-IO.print(Num != 123)  // expect: true
-IO.print(Num != true) // expect: true
+System.print(Num != 123)  // expect: true
+System.print(Num != true) // expect: true
diff --git a/test/core/class/name.wren b/test/core/class/name.wren
index f2b561a8..2f36c2e1 100644
--- a/test/core/class/name.wren
+++ b/test/core/class/name.wren
@@ -1,13 +1,13 @@
 class Foo {}
 
-IO.print(Foo.name) // expect: Foo
-IO.print(Foo.type.name) // expect: Foo metaclass
+System.print(Foo.name) // expect: Foo
+System.print(Foo.type.name) // expect: Foo metaclass
 
 // Make sure the built-in classes have proper names too.
-IO.print(Object.name) // expect: Object
-IO.print(Bool.name) // expect: Bool
-IO.print(Class.name) // expect: Class
+System.print(Object.name) // expect: Object
+System.print(Bool.name) // expect: Bool
+System.print(Class.name) // expect: Class
 
 // And metaclass names.
-IO.print(Object.type.name) // expect: Object metaclass
-IO.print(Bool.type.name) // expect: Bool metaclass
+System.print(Object.type.name) // expect: Object metaclass
+System.print(Bool.type.name) // expect: Bool metaclass
diff --git a/test/core/class/supertype.wren b/test/core/class/supertype.wren
index 9705c188..c24549b2 100644
--- a/test/core/class/supertype.wren
+++ b/test/core/class/supertype.wren
@@ -5,11 +5,11 @@ class Bar is Foo {}
 class Baz is Bar {}
 
 // A class with no explicit superclass inherits Object.
-IO.print(Foo.supertype == Object) // expect: true
+System.print(Foo.supertype == Object) // expect: true
 
 // Otherwise, it's the superclass.
-IO.print(Bar.supertype == Foo) // expect: true
-IO.print(Baz.supertype == Bar) // expect: true
+System.print(Bar.supertype == Foo) // expect: true
+System.print(Baz.supertype == Bar) // expect: true
 
 // Object has no supertype.
-IO.print(Object.supertype) // expect: null
+System.print(Object.supertype) // expect: null
diff --git a/test/core/class/type.wren b/test/core/class/type.wren
index 5ec7dd38..0c2266a0 100644
--- a/test/core/class/type.wren
+++ b/test/core/class/type.wren
@@ -1,15 +1,15 @@
 class Foo {}
 
 // A class is a class.
-IO.print(Foo is Class) // expect: true
+System.print(Foo is Class) // expect: true
 
 // Its metatype is also a class.
-IO.print(Foo.type is Class) // expect: true
+System.print(Foo.type is Class) // expect: true
 
 // The metatype's metatype is Class.
-IO.print(Foo.type.type == Class) // expect: true
+System.print(Foo.type.type == Class) // expect: true
 
 // And Class's metatype circles back onto itself.
-IO.print(Foo.type.type.type == Class) // expect: true
-IO.print(Foo.type.type.type.type == Class) // expect: true
-IO.print(Foo.type.type.type.type.type == Class) // expect: true
+System.print(Foo.type.type.type == Class) // expect: true
+System.print(Foo.type.type.type.type == Class) // expect: true
+System.print(Foo.type.type.type.type.type == Class) // expect: true
diff --git a/test/core/fiber/abort.wren b/test/core/fiber/abort.wren
index 2823ede3..1f63d325 100644
--- a/test/core/fiber/abort.wren
+++ b/test/core/fiber/abort.wren
@@ -2,6 +2,6 @@ var fiber = Fiber.new {
   Fiber.abort("Error message.")
 }
 
-IO.print(fiber.try()) // expect: Error message.
-IO.print(fiber.isDone) // expect: true
-IO.print(fiber.error) // expect: Error message.
+System.print(fiber.try()) // expect: Error message.
+System.print(fiber.isDone) // expect: true
+System.print(fiber.error) // expect: Error message.
diff --git a/test/core/fiber/call.wren b/test/core/fiber/call.wren
index 7ad0b832..6339f273 100644
--- a/test/core/fiber/call.wren
+++ b/test/core/fiber/call.wren
@@ -1,7 +1,7 @@
 var fiber = Fiber.new {
-  IO.print("fiber")
+  System.print("fiber")
 }
 
-IO.print("before") // expect: before
+System.print("before") // expect: before
 fiber.call()       // expect: fiber
-IO.print("after")  // expect: after
+System.print("after")  // expect: after
diff --git a/test/core/fiber/call_done.wren b/test/core/fiber/call_done.wren
index 894a803f..9839bd08 100644
--- a/test/core/fiber/call_done.wren
+++ b/test/core/fiber/call_done.wren
@@ -1,5 +1,5 @@
 var fiber = Fiber.new {
-  IO.print("call")
+  System.print("call")
 }
 
 fiber.call() // expect: call
diff --git a/test/core/fiber/call_error.wren b/test/core/fiber/call_error.wren
index 57742ec9..5f05436a 100644
--- a/test/core/fiber/call_error.wren
+++ b/test/core/fiber/call_error.wren
@@ -1,6 +1,6 @@
 var fiber = Fiber.new {
   Fiber.abort("Error!")
-  IO.print("should not get here")
+  System.print("should not get here")
 }
 
 fiber.try()
diff --git a/test/core/fiber/call_return_implicit_null.wren b/test/core/fiber/call_return_implicit_null.wren
index 0ce9a9a0..9464ba13 100644
--- a/test/core/fiber/call_return_implicit_null.wren
+++ b/test/core/fiber/call_return_implicit_null.wren
@@ -1,5 +1,5 @@
 var fiber = Fiber.new {
-  IO.print("fiber") // expect: fiber
+  System.print("fiber") // expect: fiber
 }
 
-IO.print(fiber.call()) // expect: null
+System.print(fiber.call()) // expect: null
diff --git a/test/core/fiber/call_return_value.wren b/test/core/fiber/call_return_value.wren
index c4dd58d9..6e0b70ef 100644
--- a/test/core/fiber/call_return_value.wren
+++ b/test/core/fiber/call_return_value.wren
@@ -1,6 +1,6 @@
 var fiber = Fiber.new {
-  IO.print("fiber")
+  System.print("fiber")
   return "result" // expect: fiber
 }
 
-IO.print(fiber.call()) // expect: result
+System.print(fiber.call()) // expect: result
diff --git a/test/core/fiber/call_transferred.wren b/test/core/fiber/call_transferred.wren
index b174ae54..11c5248b 100644
--- a/test/core/fiber/call_transferred.wren
+++ b/test/core/fiber/call_transferred.wren
@@ -1,12 +1,12 @@
 var main = Fiber.current
 
 var fiber = Fiber.new {
-  IO.print("transferred")
-  IO.print(main.transfer())
-  IO.print("called")
+  System.print("transferred")
+  System.print(main.transfer())
+  System.print("called")
 }
 
 fiber.transfer() // expect: transferred
-IO.print("main") // expect: main
+System.print("main") // expect: main
 fiber.call()     // expect: null
                  // expect: called
diff --git a/test/core/fiber/call_with_value.wren b/test/core/fiber/call_with_value.wren
index 10c905f8..2008bed2 100644
--- a/test/core/fiber/call_with_value.wren
+++ b/test/core/fiber/call_with_value.wren
@@ -1,9 +1,9 @@
 var fiber = Fiber.new {
-  IO.print("fiber")
+  System.print("fiber")
 }
 
 // The first value passed to the fiber is ignored, since there's no yield call
 // to return it.
-IO.print("before")    // expect: before
+System.print("before")    // expect: before
 fiber.call("ignored") // expect: fiber
-IO.print("after")     // expect: after
+System.print("after")     // expect: after
diff --git a/test/core/fiber/call_with_value_done.wren b/test/core/fiber/call_with_value_done.wren
index 491a7f6e..715e235e 100644
--- a/test/core/fiber/call_with_value_done.wren
+++ b/test/core/fiber/call_with_value_done.wren
@@ -1,5 +1,5 @@
 var fiber = Fiber.new {
-  IO.print("call")
+  System.print("call")
 }
 
 fiber.call(1) // expect: call
diff --git a/test/core/fiber/call_with_value_error.wren b/test/core/fiber/call_with_value_error.wren
index e5513755..e4280cb0 100644
--- a/test/core/fiber/call_with_value_error.wren
+++ b/test/core/fiber/call_with_value_error.wren
@@ -1,6 +1,6 @@
 var fiber = Fiber.new {
   Fiber.abort("Error!")
-  IO.print("should not get here")
+  System.print("should not get here")
 }
 
 fiber.try()
diff --git a/test/core/fiber/call_with_value_transferred.wren b/test/core/fiber/call_with_value_transferred.wren
index b0e1cc99..aa52b2f4 100644
--- a/test/core/fiber/call_with_value_transferred.wren
+++ b/test/core/fiber/call_with_value_transferred.wren
@@ -1,12 +1,12 @@
 var main = Fiber.current
 
 var fiber = Fiber.new {
-  IO.print("transferred")
-  IO.print(main.transfer())
-  IO.print("called")
+  System.print("transferred")
+  System.print(main.transfer())
+  System.print("called")
 }
 
 fiber.transfer()    // expect: transferred
-IO.print("main")    // expect: main
+System.print("main")    // expect: main
 fiber.call("value") // expect: value
                     // expect: called
diff --git a/test/core/fiber/error.wren b/test/core/fiber/error.wren
index f6087d98..3ec0374b 100644
--- a/test/core/fiber/error.wren
+++ b/test/core/fiber/error.wren
@@ -2,6 +2,6 @@ var fiber = Fiber.new {
   "s".unknown
 }
 
-IO.print(fiber.error) // expect: null
-IO.print(fiber.try()) // expect: String does not implement 'unknown'.
-IO.print(fiber.error) // expect: String does not implement 'unknown'.
+System.print(fiber.error) // expect: null
+System.print(fiber.try()) // expect: String does not implement 'unknown'.
+System.print(fiber.error) // expect: String does not implement 'unknown'.
diff --git a/test/core/fiber/is_done.wren b/test/core/fiber/is_done.wren
index f4d500b8..941d5a63 100644
--- a/test/core/fiber/is_done.wren
+++ b/test/core/fiber/is_done.wren
@@ -1,11 +1,11 @@
 var fiber = Fiber.new {
-  IO.print("1")
+  System.print("1")
   Fiber.yield()
-  IO.print("2")
+  System.print("2")
 }
 
-IO.print(fiber.isDone)  // expect: false
+System.print(fiber.isDone)  // expect: false
 fiber.call()            // expect: 1
-IO.print(fiber.isDone)  // expect: false
+System.print(fiber.isDone)  // expect: false
 fiber.call()            // expect: 2
-IO.print(fiber.isDone)  // expect: true
+System.print(fiber.isDone)  // expect: true
diff --git a/test/core/fiber/is_done_after_error.wren b/test/core/fiber/is_done_after_error.wren
index 479b8d3c..4fd33093 100644
--- a/test/core/fiber/is_done_after_error.wren
+++ b/test/core/fiber/is_done_after_error.wren
@@ -3,4 +3,4 @@ var fiber = Fiber.new {
 }
 
 fiber.try()
-IO.print(fiber.isDone) // expect: true
+System.print(fiber.isDone) // expect: true
diff --git a/test/core/fiber/resume_caller.wren b/test/core/fiber/resume_caller.wren
index 64a726db..31c34072 100644
--- a/test/core/fiber/resume_caller.wren
+++ b/test/core/fiber/resume_caller.wren
@@ -1,16 +1,16 @@
 var b = Fiber.new {
-  IO.print("fiber b")
+  System.print("fiber b")
 }
 
 var a = Fiber.new {
-  IO.print("begin fiber a")
+  System.print("begin fiber a")
   b.call()
-  IO.print("end fiber a")
+  System.print("end fiber a")
 }
 
-IO.print("begin main")
+System.print("begin main")
 a.call()
-IO.print("end main")
+System.print("end main")
 
 // expect: begin main
 // expect: begin fiber a
diff --git a/test/core/fiber/transfer.wren b/test/core/fiber/transfer.wren
index b97fe109..b4284f8c 100644
--- a/test/core/fiber/transfer.wren
+++ b/test/core/fiber/transfer.wren
@@ -1,20 +1,20 @@
 var a = Fiber.new {
-  IO.print("a")
+  System.print("a")
 }
 
 var b = Fiber.new {
-  IO.print("b before")
+  System.print("b before")
   a.transfer()
-  IO.print("b after")
+  System.print("b after")
 }
 
 var c = Fiber.new {
-  IO.print("c before")
+  System.print("c before")
   b.transfer()
-  IO.print("c after")
+  System.print("c after")
 }
 
-IO.print("start") // expect: start
+System.print("start") // expect: start
 
 c.transfer()
 // expect: c before
diff --git a/test/core/fiber/transfer_direct_reenter.wren b/test/core/fiber/transfer_direct_reenter.wren
index ce424e0d..66559330 100644
--- a/test/core/fiber/transfer_direct_reenter.wren
+++ b/test/core/fiber/transfer_direct_reenter.wren
@@ -1,9 +1,9 @@
 var F = Fiber.new {
-  IO.print(1)            // expect: 1
-  IO.print(F.transfer()) // expect: null
-  IO.print(2)            // expect: 2
+  System.print(1)            // expect: 1
+  System.print(F.transfer()) // expect: null
+  System.print(2)            // expect: 2
 }
 
 F.call()
 // F remembers its original caller so transfers back to main.
-IO.print(3) // expect: 3
+System.print(3) // expect: 3
diff --git a/test/core/fiber/transfer_indirect_reenter.wren b/test/core/fiber/transfer_indirect_reenter.wren
index 2a2cfaff..763867ef 100644
--- a/test/core/fiber/transfer_indirect_reenter.wren
+++ b/test/core/fiber/transfer_indirect_reenter.wren
@@ -1,13 +1,13 @@
 var A = Fiber.new {
-  IO.print(2)
+  System.print(2)
   B.transfer()
-  IO.print("nope")
+  System.print("nope")
 }
 
 var B = Fiber.new {
-  IO.print(1)
+  System.print(1)
   A.transfer()
-  IO.print(3)
+  System.print(3)
 }
 
 B.call()
@@ -15,4 +15,4 @@ B.call()
 // expect: 2
 // expect: 3
 // B remembers its original caller so returns to main.
-IO.print(4) // expect: 4
+System.print(4) // expect: 4
diff --git a/test/core/fiber/transfer_return_call_value.wren b/test/core/fiber/transfer_return_call_value.wren
index b12b9261..838597e6 100644
--- a/test/core/fiber/transfer_return_call_value.wren
+++ b/test/core/fiber/transfer_return_call_value.wren
@@ -1,23 +1,23 @@
 var main = Fiber.current
 
 var fiber = Fiber.new {
-  IO.print("fiber 1")
-  IO.print(main.transfer())
+  System.print("fiber 1")
+  System.print(main.transfer())
 
   // Yield to bounce back to main and clear the caller so we don't get a
   // double call() error below.
   Fiber.yield()
 
-  IO.print(main.transfer())
+  System.print(main.transfer())
 }
 
 fiber.transfer() // expect: fiber 1
-IO.print("main 1") // expect: main 1
+System.print("main 1") // expect: main 1
 fiber.call("call 1") // expect: call 1
 
-IO.print("main 2") // expect: main 2
+System.print("main 2") // expect: main 2
 // Transfer back into the fiber so it has a NULL caller.
 fiber.transfer()
 
 fiber.call() // expect: null
-IO.print("main 3") // expect: main 3
+System.print("main 3") // expect: main 3
diff --git a/test/core/fiber/transfer_return_transfer_value.wren b/test/core/fiber/transfer_return_transfer_value.wren
index 9bde5a0f..a8338692 100644
--- a/test/core/fiber/transfer_return_transfer_value.wren
+++ b/test/core/fiber/transfer_return_transfer_value.wren
@@ -1,13 +1,13 @@
 var main = Fiber.current
 
 var fiber = Fiber.new {
-  IO.print("fiber")
-  IO.print(main.transfer())
+  System.print("fiber")
+  System.print(main.transfer())
 }
 
 fiber.transfer() // expect: fiber
-IO.print("main") // expect: main
+System.print("main") // expect: main
 fiber.transfer("transfer") // expect: transfer
 
 // This does not get run since we exit when the transferred fiber completes.
-IO.print("nope")
+System.print("nope")
diff --git a/test/core/fiber/transfer_to_done.wren b/test/core/fiber/transfer_to_done.wren
index 8e330850..f5eb0de7 100644
--- a/test/core/fiber/transfer_to_done.wren
+++ b/test/core/fiber/transfer_to_done.wren
@@ -1,5 +1,5 @@
 var a = Fiber.new {
-  IO.print("run")
+  System.print("run")
 }
 
 a.call() // expect: run
diff --git a/test/core/fiber/transfer_to_error.wren b/test/core/fiber/transfer_to_error.wren
index c50e770b..18dae072 100644
--- a/test/core/fiber/transfer_to_error.wren
+++ b/test/core/fiber/transfer_to_error.wren
@@ -1,6 +1,6 @@
 var a = Fiber.new {
   Fiber.abort("Error!")
-  IO.print("should not get here")
+  System.print("should not get here")
 }
 
 a.try()
diff --git a/test/core/fiber/transfer_to_yielded.wren b/test/core/fiber/transfer_to_yielded.wren
index f74f1526..a03de88b 100644
--- a/test/core/fiber/transfer_to_yielded.wren
+++ b/test/core/fiber/transfer_to_yielded.wren
@@ -1,7 +1,7 @@
 var fiber = Fiber.new {
-  IO.print("called")
-  IO.print(Fiber.yield())
-  IO.print("transferred")
+  System.print("called")
+  System.print(Fiber.yield())
+  System.print("transferred")
 }
 
 fiber.call()     // expect: called
diff --git a/test/core/fiber/transfer_with_value.wren b/test/core/fiber/transfer_with_value.wren
index efe8f956..9d60a707 100644
--- a/test/core/fiber/transfer_with_value.wren
+++ b/test/core/fiber/transfer_with_value.wren
@@ -1,20 +1,20 @@
 var a = Fiber.new {
-  IO.print("a")
+  System.print("a")
 }
 
 var b = Fiber.new {
-  IO.print("b before")
+  System.print("b before")
   a.transfer("ignored")
-  IO.print("b after")
+  System.print("b after")
 }
 
 var c = Fiber.new {
-  IO.print("c before")
+  System.print("c before")
   b.transfer("ignored")
-  IO.print("c after")
+  System.print("c after")
 }
 
-IO.print("start") // expect: start
+System.print("start") // expect: start
 
 c.transfer("ignored")
 // expect: c before
diff --git a/test/core/fiber/transfer_with_value_direct_reenter.wren b/test/core/fiber/transfer_with_value_direct_reenter.wren
index b5b92b1f..1fb7ae18 100644
--- a/test/core/fiber/transfer_with_value_direct_reenter.wren
+++ b/test/core/fiber/transfer_with_value_direct_reenter.wren
@@ -1,8 +1,8 @@
 var F = Fiber.new {
-  IO.print(1) // expect: 1
-  IO.print(F.transfer("value")) // expect: value
-  IO.print(2) // expect: 2
+  System.print(1) // expect: 1
+  System.print(F.transfer("value")) // expect: value
+  System.print(2) // expect: 2
 }
 
 F.call()
-IO.print(3) // expect: 3
+System.print(3) // expect: 3
diff --git a/test/core/fiber/transfer_with_value_indirect_reenter.wren b/test/core/fiber/transfer_with_value_indirect_reenter.wren
index d98092c6..2423a152 100644
--- a/test/core/fiber/transfer_with_value_indirect_reenter.wren
+++ b/test/core/fiber/transfer_with_value_indirect_reenter.wren
@@ -1,17 +1,17 @@
 var A = Fiber.new {
-  IO.print(2)
+  System.print(2)
   B.transfer("ignored")
-  IO.print("nope")
+  System.print("nope")
 }
 
 var B = Fiber.new {
-  IO.print(1)
+  System.print(1)
   A.transfer("ignored")
-  IO.print(3)
+  System.print(3)
 }
 
 B.call()
 // expect: 1
 // expect: 2
 // expect: 3
-IO.print(4) // expect: 4
+System.print(4) // expect: 4
diff --git a/test/core/fiber/transfer_with_value_to_done.wren b/test/core/fiber/transfer_with_value_to_done.wren
index 980b6e11..c156ce7e 100644
--- a/test/core/fiber/transfer_with_value_to_done.wren
+++ b/test/core/fiber/transfer_with_value_to_done.wren
@@ -1,5 +1,5 @@
 var a = Fiber.new {
-  IO.print("run")
+  System.print("run")
 }
 
 a.call() // expect: run
diff --git a/test/core/fiber/transfer_with_value_to_error.wren b/test/core/fiber/transfer_with_value_to_error.wren
index f8ec2f97..3a458503 100644
--- a/test/core/fiber/transfer_with_value_to_error.wren
+++ b/test/core/fiber/transfer_with_value_to_error.wren
@@ -1,6 +1,6 @@
 var a = Fiber.new {
   Fiber.abort("Error!")
-  IO.print("should not get here")
+  System.print("should not get here")
 }
 
 a.try()
diff --git a/test/core/fiber/transfer_with_value_to_yielded.wren b/test/core/fiber/transfer_with_value_to_yielded.wren
index 016dc790..4bf807f7 100644
--- a/test/core/fiber/transfer_with_value_to_yielded.wren
+++ b/test/core/fiber/transfer_with_value_to_yielded.wren
@@ -1,7 +1,7 @@
 var fiber = Fiber.new {
-  IO.print("called")
-  IO.print(Fiber.yield())
-  IO.print("transferred")
+  System.print("called")
+  System.print(Fiber.yield())
+  System.print("transferred")
 }
 
 fiber.call()            // expect: called
diff --git a/test/core/fiber/try.wren b/test/core/fiber/try.wren
index dbb5582e..51d065fd 100644
--- a/test/core/fiber/try.wren
+++ b/test/core/fiber/try.wren
@@ -1,10 +1,10 @@
 var fiber = Fiber.new {
-  IO.print("before")
+  System.print("before")
   true.unknownMethod
-  IO.print("after")
+  System.print("after")
 }
 
-IO.print(fiber.try())
+System.print(fiber.try())
 // expect: before
 // expect: Bool does not implement 'unknownMethod'.
-IO.print("after try") // expect: after try
+System.print("after try") // expect: after try
diff --git a/test/core/fiber/try_when_done.wren b/test/core/fiber/try_when_done.wren
index 180d9d95..40d4d928 100644
--- a/test/core/fiber/try_when_done.wren
+++ b/test/core/fiber/try_when_done.wren
@@ -1,5 +1,5 @@
 var fiber = Fiber.new {
-  IO.print("try")
+  System.print("try")
 }
 
 fiber.try() // expect: try
diff --git a/test/core/fiber/try_without_error.wren b/test/core/fiber/try_without_error.wren
index c9314303..c84a13dc 100644
--- a/test/core/fiber/try_without_error.wren
+++ b/test/core/fiber/try_without_error.wren
@@ -1,8 +1,8 @@
 var fiber = Fiber.new {
-  IO.print("fiber")
+  System.print("fiber")
 }
 
-IO.print("before")    // expect: before
-IO.print(fiber.try()) // expect: fiber
+System.print("before")    // expect: before
+System.print(fiber.try()) // expect: fiber
                       // expect: null
-IO.print("after")     // expect: after
+System.print("after")     // expect: after
diff --git a/test/core/fiber/type.wren b/test/core/fiber/type.wren
index 49da2437..39c946ce 100644
--- a/test/core/fiber/type.wren
+++ b/test/core/fiber/type.wren
@@ -1,5 +1,5 @@
 var fiber = Fiber.new {}
-IO.print(fiber is Fiber)      // expect: true
-IO.print(fiber is Object)     // expect: true
-IO.print(fiber is Bool)       // expect: false
-IO.print(fiber.type == Fiber) // expect: true
+System.print(fiber is Fiber)      // expect: true
+System.print(fiber is Object)     // expect: true
+System.print(fiber is Bool)       // expect: false
+System.print(fiber.type == Fiber) // expect: true
diff --git a/test/core/fiber/yield.wren b/test/core/fiber/yield.wren
index ea4491c1..868a74e2 100644
--- a/test/core/fiber/yield.wren
+++ b/test/core/fiber/yield.wren
@@ -1,14 +1,14 @@
 var fiber = Fiber.new {
-  IO.print("fiber 1")
+  System.print("fiber 1")
   Fiber.yield()
-  IO.print("fiber 2")
+  System.print("fiber 2")
   Fiber.yield()
-  IO.print("fiber 3")
+  System.print("fiber 3")
 }
 
 fiber.call()          // expect: fiber 1
-IO.print("main 1")    // expect: main 1
+System.print("main 1")    // expect: main 1
 fiber.call()          // expect: fiber 2
-IO.print("main 2")    // expect: main 2
+System.print("main 2")    // expect: main 2
 fiber.call()          // expect: fiber 3
-IO.print("main 3")    // expect: main 3
+System.print("main 3")    // expect: main 3
diff --git a/test/core/fiber/yield_from_main.wren b/test/core/fiber/yield_from_main.wren
index bea7be34..3bc7e5aa 100644
--- a/test/core/fiber/yield_from_main.wren
+++ b/test/core/fiber/yield_from_main.wren
@@ -1,3 +1,3 @@
-IO.print("before") // expect: before
+System.print("before") // expect: before
 Fiber.yield()
-IO.print("not reached")
+System.print("not reached")
diff --git a/test/core/fiber/yield_return_call_value.wren b/test/core/fiber/yield_return_call_value.wren
index b858fd26..d464ec20 100644
--- a/test/core/fiber/yield_return_call_value.wren
+++ b/test/core/fiber/yield_return_call_value.wren
@@ -1,12 +1,12 @@
 var fiber = Fiber.new {
-  IO.print("fiber 1")
-  IO.print(Fiber.yield())
-  IO.print(Fiber.yield())
+  System.print("fiber 1")
+  System.print(Fiber.yield())
+  System.print(Fiber.yield())
 }
 
 fiber.call() // expect: fiber 1
-IO.print("main 1") // expect: main 1
+System.print("main 1") // expect: main 1
 fiber.call("call 1") // expect: call 1
-IO.print("main 2") // expect: main 2
+System.print("main 2") // expect: main 2
 fiber.call() // expect: null
-IO.print("main 3") // expect: main 3
+System.print("main 3") // expect: main 3
diff --git a/test/core/fiber/yield_return_transfer_value.wren b/test/core/fiber/yield_return_transfer_value.wren
index a345ea7c..c8b85642 100644
--- a/test/core/fiber/yield_return_transfer_value.wren
+++ b/test/core/fiber/yield_return_transfer_value.wren
@@ -1,13 +1,13 @@
 var main = Fiber.current
 
 var a = Fiber.new {
-  IO.print("a")
-  IO.print(Fiber.yield())
+  System.print("a")
+  System.print(Fiber.yield())
 }
 
 var b = Fiber.new {
-  IO.print("b")
-  IO.print(Fiber.yield())
+  System.print("b")
+  System.print(Fiber.yield())
 
   a.call()
   a.transfer("value")
diff --git a/test/core/fiber/yield_with_no_caller.wren b/test/core/fiber/yield_with_no_caller.wren
index 49b975c2..aa1a4aa6 100644
--- a/test/core/fiber/yield_with_no_caller.wren
+++ b/test/core/fiber/yield_with_no_caller.wren
@@ -1,7 +1,7 @@
 var a = Fiber.new {
-  IO.print("before") // expect: before
+  System.print("before") // expect: before
   Fiber.yield()
-  IO.print("not reached")
+  System.print("not reached")
 }
 
 // Transfer through a chain of fibers. Since none of them are called, they all
@@ -9,4 +9,4 @@ var a = Fiber.new {
 var b = Fiber.new { a.transfer() }
 var c = Fiber.new { b.transfer() }
 c.transfer()
-IO.print("not reached")
\ No newline at end of file
+System.print("not reached")
\ No newline at end of file
diff --git a/test/core/fiber/yield_with_value.wren b/test/core/fiber/yield_with_value.wren
index 979c3c81..8995ef54 100644
--- a/test/core/fiber/yield_with_value.wren
+++ b/test/core/fiber/yield_with_value.wren
@@ -1,14 +1,14 @@
 var fiber = Fiber.new {
-  IO.print("fiber 1")
+  System.print("fiber 1")
   Fiber.yield("yield 1")
-  IO.print("fiber 2")
+  System.print("fiber 2")
   Fiber.yield("yield 2")
-  IO.print("fiber 3")
+  System.print("fiber 3")
 }
 
-IO.print(fiber.call())  // expect: fiber 1
+System.print(fiber.call())  // expect: fiber 1
                         // expect: yield 1
-IO.print(fiber.call())  // expect: fiber 2
+System.print(fiber.call())  // expect: fiber 2
                         // expect: yield 2
-IO.print(fiber.call())  // expect: fiber 3
+System.print(fiber.call())  // expect: fiber 3
                         // expect: null
diff --git a/test/core/fiber/yield_with_value_from_main.wren b/test/core/fiber/yield_with_value_from_main.wren
index f535a7b8..3306e537 100644
--- a/test/core/fiber/yield_with_value_from_main.wren
+++ b/test/core/fiber/yield_with_value_from_main.wren
@@ -1,3 +1,3 @@
-IO.print("before") // expect: before
+System.print("before") // expect: before
 Fiber.yield(1)
-IO.print("not reached")
\ No newline at end of file
+System.print("not reached")
\ No newline at end of file
diff --git a/test/core/fiber/yield_with_value_with_no_caller.wren b/test/core/fiber/yield_with_value_with_no_caller.wren
index 615e96cd..388749a7 100644
--- a/test/core/fiber/yield_with_value_with_no_caller.wren
+++ b/test/core/fiber/yield_with_value_with_no_caller.wren
@@ -1,7 +1,7 @@
 var a = Fiber.new {
-  IO.print("before") // expect: before
+  System.print("before") // expect: before
   Fiber.yield(1)
-  IO.print("not reached")
+  System.print("not reached")
 }
 
 // Transfer through a chain of fibers. Since none of them are called, they all
@@ -9,4 +9,4 @@ var a = Fiber.new {
 var b = Fiber.new { a.transfer() }
 var c = Fiber.new { b.transfer() }
 c.transfer()
-IO.print("not reached")
+System.print("not reached")
diff --git a/test/core/function/arity.wren b/test/core/function/arity.wren
index ab40eff9..3329cc99 100644
--- a/test/core/function/arity.wren
+++ b/test/core/function/arity.wren
@@ -1,5 +1,5 @@
-IO.print(Fn.new {}.arity) // expect: 0
-IO.print(Fn.new {|a| a}.arity) // expect: 1
-IO.print(Fn.new {|a, b| a}.arity) // expect: 2
-IO.print(Fn.new {|a, b, c| a}.arity) // expect: 3
-IO.print(Fn.new {|a, b, c, d| a}.arity) // expect: 4
+System.print(Fn.new {}.arity) // expect: 0
+System.print(Fn.new {|a| a}.arity) // expect: 1
+System.print(Fn.new {|a, b| a}.arity) // expect: 2
+System.print(Fn.new {|a, b, c| a}.arity) // expect: 3
+System.print(Fn.new {|a, b, c, d| a}.arity) // expect: 4
diff --git a/test/core/function/call_extra_arguments.wren b/test/core/function/call_extra_arguments.wren
index f183576f..2a0c22bd 100644
--- a/test/core/function/call_extra_arguments.wren
+++ b/test/core/function/call_extra_arguments.wren
@@ -1,7 +1,7 @@
-var f0 = Fn.new { IO.print("zero") }
-var f1 = Fn.new {|a| IO.print("one ", a) }
-var f2 = Fn.new {|a, b| IO.print("two ", a, " ", b) }
-var f3 = Fn.new {|a, b, c| IO.print("three ", a, " ", b, " ", c) }
+var f0 = Fn.new { System.print("zero") }
+var f1 = Fn.new {|a| System.print("one " + a) }
+var f2 = Fn.new {|a, b| System.print("two " + a + " " + b) }
+var f3 = Fn.new {|a, b, c| System.print("three " + a + " " + b + " " + c) }
 
 f0.call("a") // expect: zero
 f0.call("a", "b") // expect: zero
diff --git a/test/core/function/call_missing_arguments.wren b/test/core/function/call_missing_arguments.wren
index 162623c9..3f7b47b4 100644
--- a/test/core/function/call_missing_arguments.wren
+++ b/test/core/function/call_missing_arguments.wren
@@ -1,2 +1,2 @@
-var f2 = Fn.new {|a, b| IO.print(a, b) }
+var f2 = Fn.new {|a, b| System.print(a, b) }
 f2.call("a") // expect runtime error: Function expects more arguments.
diff --git a/test/core/function/equality.wren b/test/core/function/equality.wren
index 29239518..2164915b 100644
--- a/test/core/function/equality.wren
+++ b/test/core/function/equality.wren
@@ -1,16 +1,16 @@
 // Not structurally equal.
-IO.print(Fn.new { 123 } == Fn.new { 123 })  // expect: false
-IO.print(Fn.new { 123 } != Fn.new { 123 })  // expect: true
+System.print(Fn.new { 123 } == Fn.new { 123 })  // expect: false
+System.print(Fn.new { 123 } != Fn.new { 123 })  // expect: true
 
 // Not equal to other types.
-IO.print(Fn.new { 123 } == 1)         // expect: false
-IO.print(Fn.new { 123 } == false)     // expect: false
-IO.print(Fn.new { 123 } == "fn 123")  // expect: false
-IO.print(Fn.new { 123 } != 1)         // expect: true
-IO.print(Fn.new { 123 } != false)     // expect: true
-IO.print(Fn.new { 123 } != "fn 123")  // expect: true
+System.print(Fn.new { 123 } == 1)         // expect: false
+System.print(Fn.new { 123 } == false)     // expect: false
+System.print(Fn.new { 123 } == "fn 123")  // expect: false
+System.print(Fn.new { 123 } != 1)         // expect: true
+System.print(Fn.new { 123 } != false)     // expect: true
+System.print(Fn.new { 123 } != "fn 123")  // expect: true
 
 // Equal by identity.
 var f = Fn.new { 123 }
-IO.print(f == f) // expect: true
-IO.print(f != f) // expect: false
+System.print(f == f) // expect: true
+System.print(f != f) // expect: false
diff --git a/test/core/function/to_string.wren b/test/core/function/to_string.wren
index 8a72cbe3..e78807ea 100644
--- a/test/core/function/to_string.wren
+++ b/test/core/function/to_string.wren
@@ -1 +1 @@
-IO.print(Fn.new {}) // expect: <fn>
+System.print(Fn.new {}) // expect: <fn>
diff --git a/test/core/function/type.wren b/test/core/function/type.wren
index 429d9e37..9cd00a16 100644
--- a/test/core/function/type.wren
+++ b/test/core/function/type.wren
@@ -1,4 +1,4 @@
-IO.print(Fn.new { 0 } is Fn)      // expect: true
-IO.print(Fn.new { 0 } is Object)  // expect: true
-IO.print(Fn.new { 0 } is String)  // expect: false
-IO.print(Fn.new { 0 }.type == Fn) // expect: true
+System.print(Fn.new { 0 } is Fn)      // expect: true
+System.print(Fn.new { 0 } is Object)  // expect: true
+System.print(Fn.new { 0 } is String)  // expect: false
+System.print(Fn.new { 0 }.type == Fn) // expect: true
diff --git a/test/core/list/add.wren b/test/core/list/add.wren
index 33025499..3a2c0b86 100644
--- a/test/core/list/add.wren
+++ b/test/core/list/add.wren
@@ -1,8 +1,8 @@
 var a = [1]
 a.add(2)
-IO.print(a) // expect: [1, 2]
+System.print(a) // expect: [1, 2]
 a.add(3)
-IO.print(a) // expect: [1, 2, 3]
+System.print(a) // expect: [1, 2, 3]
 
 // Returns added element.
-IO.print(a.add(4)) // expect: 4
+System.print(a.add(4)) // expect: 4
diff --git a/test/core/list/add_all.wren b/test/core/list/add_all.wren
index 1d79b852..bdfae735 100644
--- a/test/core/list/add_all.wren
+++ b/test/core/list/add_all.wren
@@ -1,11 +1,11 @@
 var a = [1]
 a.addAll([2, 3])
-IO.print(a) // expect: [1, 2, 3]
+System.print(a) // expect: [1, 2, 3]
 a.addAll([])
-IO.print(a) // expect: [1, 2, 3]
+System.print(a) // expect: [1, 2, 3]
 a.addAll(4..6)
-IO.print(a) // expect: [1, 2, 3, 4, 5, 6]
+System.print(a) // expect: [1, 2, 3, 4, 5, 6]
 
 // Returns argument.
 var range = 7..9
-IO.print(a.addAll(range) == range) // expect: true
+System.print(a.addAll(range) == range) // expect: true
diff --git a/test/core/list/clear.wren b/test/core/list/clear.wren
index 6f76a558..a093abe7 100644
--- a/test/core/list/clear.wren
+++ b/test/core/list/clear.wren
@@ -1,7 +1,7 @@
 var a = [1, 2, 3]
 a.clear()
-IO.print(a)       // expect: []
-IO.print(a.count) // expect: 0
+System.print(a)       // expect: []
+System.print(a.count) // expect: 0
 
 // Returns null.
-IO.print([1, 2].clear()) // expect: null
+System.print([1, 2].clear()) // expect: null
diff --git a/test/core/list/contains.wren b/test/core/list/contains.wren
index 8ceae4d0..9e13364b 100644
--- a/test/core/list/contains.wren
+++ b/test/core/list/contains.wren
@@ -1,6 +1,6 @@
 var list = [1, 2, 3, 4, "foo"]
 
-IO.print(list.contains(2))      // expect: true
-IO.print(list.contains(5))      // expect: false
-IO.print(list.contains("foo"))  // expect: true
-IO.print(list.contains("bar"))  // expect: false
+System.print(list.contains(2))      // expect: true
+System.print(list.contains(5))      // expect: false
+System.print(list.contains("foo"))  // expect: true
+System.print(list.contains("bar"))  // expect: false
diff --git a/test/core/list/count.wren b/test/core/list/count.wren
index 9b5c2f10..8d40c5bc 100644
--- a/test/core/list/count.wren
+++ b/test/core/list/count.wren
@@ -1,3 +1,3 @@
-IO.print([].count)           // expect: 0
-IO.print([1].count)          // expect: 1
-IO.print([1, 2, 3, 4].count) // expect: 4
+System.print([].count)           // expect: 0
+System.print([1].count)          // expect: 1
+System.print([1, 2, 3, 4].count) // expect: 4
diff --git a/test/core/list/count_predicate.wren b/test/core/list/count_predicate.wren
index 349cf976..081383da 100644
--- a/test/core/list/count_predicate.wren
+++ b/test/core/list/count_predicate.wren
@@ -1,6 +1,6 @@
 var a = [1, 2, 3]
 
-IO.print(a.count {|x| x > 3 })      // expect: 0
-IO.print(a.count {|x| x > 1 })      // expect: 2
+System.print(a.count {|x| x > 3 })      // expect: 0
+System.print(a.count {|x| x > 1 })      // expect: 2
 
-IO.print([].count {|x| true })      // expect: 0
+System.print([].count {|x| true })      // expect: 0
diff --git a/test/core/list/count_predicate_non_bool_returning_fn.wren b/test/core/list/count_predicate_non_bool_returning_fn.wren
index 35feb0b6..c6f7a749 100644
--- a/test/core/list/count_predicate_non_bool_returning_fn.wren
+++ b/test/core/list/count_predicate_non_bool_returning_fn.wren
@@ -1,3 +1,3 @@
 var a = [1, 2, 3]
 
-IO.print(a.count {|x| "truthy" })   // expect: 3
+System.print(a.count {|x| "truthy" })   // expect: 3
diff --git a/test/core/list/each.wren b/test/core/list/each.wren
index 6629a498..20b7e49e 100644
--- a/test/core/list/each.wren
+++ b/test/core/list/each.wren
@@ -1,3 +1,3 @@
 var words = ""
 ["One", "Two", "Three"].each {|word| words = words + word }
-IO.print(words) // expect: OneTwoThree
+System.print(words) // expect: OneTwoThree
diff --git a/test/core/list/each_no_items.wren b/test/core/list/each_no_items.wren
index cc3754a9..c81f55cb 100644
--- a/test/core/list/each_no_items.wren
+++ b/test/core/list/each_no_items.wren
@@ -1,3 +1,3 @@
 var i = 0
 [].each {|item| i = i + 1 }
-IO.print(i) // expect: 0
+System.print(i) // expect: 0
diff --git a/test/core/list/insert.wren b/test/core/list/insert.wren
index ed471a60..debeb9e0 100644
--- a/test/core/list/insert.wren
+++ b/test/core/list/insert.wren
@@ -1,41 +1,41 @@
 // Add to empty list.
 var a = []
 a.insert(0, 1)
-IO.print(a) // expect: [1]
+System.print(a) // expect: [1]
 
 // Normal indices.
 var b = [1, 2, 3]
 b.insert(0, 4)
-IO.print(b) // expect: [4, 1, 2, 3]
+System.print(b) // expect: [4, 1, 2, 3]
 
 var c = [1, 2, 3]
 c.insert(1, 4)
-IO.print(c) // expect: [1, 4, 2, 3]
+System.print(c) // expect: [1, 4, 2, 3]
 
 var d = [1, 2, 3]
 d.insert(2, 4)
-IO.print(d) // expect: [1, 2, 4, 3]
+System.print(d) // expect: [1, 2, 4, 3]
 
 var e = [1, 2, 3]
 e.insert(3, 4)
-IO.print(e) // expect: [1, 2, 3, 4]
+System.print(e) // expect: [1, 2, 3, 4]
 
 // Negative indices.
 var f = [1, 2, 3]
 f.insert(-4, 4)
-IO.print(f) // expect: [4, 1, 2, 3]
+System.print(f) // expect: [4, 1, 2, 3]
 
 var g = [1, 2, 3]
 g.insert(-3, 4)
-IO.print(g) // expect: [1, 4, 2, 3]
+System.print(g) // expect: [1, 4, 2, 3]
 
 var h = [1, 2, 3]
 h.insert(-2, 4)
-IO.print(h) // expect: [1, 2, 4, 3]
+System.print(h) // expect: [1, 2, 4, 3]
 
 var i = [1, 2, 3]
 i.insert(-1, 4)
-IO.print(i) // expect: [1, 2, 3, 4]
+System.print(i) // expect: [1, 2, 3, 4]
 
 // Returns.inserted value.
-IO.print([1, 2].insert(0, 3)) // expect: 3
+System.print([1, 2].insert(0, 3)) // expect: 3
diff --git a/test/core/list/iterate.wren b/test/core/list/iterate.wren
index 14bff801..3f48de49 100644
--- a/test/core/list/iterate.wren
+++ b/test/core/list/iterate.wren
@@ -1,13 +1,13 @@
 var a = ["one", "two", "three", "four"]
-IO.print(a.iterate(null)) // expect: 0
-IO.print(a.iterate(0)) // expect: 1
-IO.print(a.iterate(1)) // expect: 2
-IO.print(a.iterate(2)) // expect: 3
-IO.print(a.iterate(3)) // expect: false
+System.print(a.iterate(null)) // expect: 0
+System.print(a.iterate(0)) // expect: 1
+System.print(a.iterate(1)) // expect: 2
+System.print(a.iterate(2)) // expect: 3
+System.print(a.iterate(3)) // expect: false
 
 // Out of bounds.
-IO.print(a.iterate(123)) // expect: false
-IO.print(a.iterate(-1)) // expect: false
+System.print(a.iterate(123)) // expect: false
+System.print(a.iterate(-1)) // expect: false
 
 // Nothing to iterate in an empty list.
-IO.print([].iterate(null)) // expect: false
+System.print([].iterate(null)) // expect: false
diff --git a/test/core/list/iterator_value.wren b/test/core/list/iterator_value.wren
index 899dbc67..093151d2 100644
--- a/test/core/list/iterator_value.wren
+++ b/test/core/list/iterator_value.wren
@@ -1,5 +1,5 @@
 var a = ["one", "two", "three", "four"]
-IO.print(a.iteratorValue(0)) // expect: one
-IO.print(a.iteratorValue(1)) // expect: two
-IO.print(a.iteratorValue(2)) // expect: three
-IO.print(a.iteratorValue(3)) // expect: four
+System.print(a.iteratorValue(0)) // expect: one
+System.print(a.iteratorValue(1)) // expect: two
+System.print(a.iteratorValue(2)) // expect: three
+System.print(a.iteratorValue(3)) // expect: four
diff --git a/test/core/list/join.wren b/test/core/list/join.wren
index 07f41333..b94b4d16 100644
--- a/test/core/list/join.wren
+++ b/test/core/list/join.wren
@@ -1,17 +1,17 @@
 // Handle empty list.
-IO.print([].join(",") == "") // expect: true
+System.print([].join(",") == "") // expect: true
 
 // Handle a simple list with an empty delimeter.
-IO.print([1, 2, 3].join("")) // expect: 123
+System.print([1, 2, 3].join("")) // expect: 123
 
 // Handle a simple list with no separator.
-IO.print([1, 2, 3].join) // expect: 123
+System.print([1, 2, 3].join) // expect: 123
 
 // Does not quote strings.
-IO.print([1, "2", true].join(",")) // expect: 1,2,true
+System.print([1, "2", true].join(",")) // expect: 1,2,true
 
 // Nested lists.
-IO.print([1, [2, [3], 4], 5].join(",")) // expect: 1,[2, [3], 4],5
+System.print([1, [2, [3], 4], 5].join(",")) // expect: 1,[2, [3], 4],5
 
 // Calls toString on elements.
 class Foo {
@@ -19,6 +19,6 @@ class Foo {
   toString { "Foo.toString" }
 }
 
-IO.print([1, Foo.new(), 2].join(", ")) // expect: 1, Foo.toString, 2
+System.print([1, Foo.new(), 2].join(", ")) // expect: 1, Foo.toString, 2
 
 // TODO: Handle lists that contain themselves.
diff --git a/test/core/list/map.wren b/test/core/list/map.wren
index d3eeed60..178b14e9 100644
--- a/test/core/list/map.wren
+++ b/test/core/list/map.wren
@@ -1,3 +1,3 @@
 var a = [1, 2, 3]
 var b = a.map {|x| x + 1 }.toList
-IO.print(b) // expect: [2, 3, 4]
+System.print(b) // expect: [2, 3, 4]
diff --git a/test/core/list/new.wren b/test/core/list/new.wren
index 2e3af0e6..061384ef 100644
--- a/test/core/list/new.wren
+++ b/test/core/list/new.wren
@@ -1,6 +1,6 @@
 var list = List.new()
 
-IO.print(list.count) // expect: 0
-IO.print(list) // expect: []
+System.print(list.count) // expect: 0
+System.print(list) // expect: []
 list.add(1)
-IO.print(list) // expect: [1]
+System.print(list) // expect: [1]
diff --git a/test/core/list/not.wren b/test/core/list/not.wren
index a6734cc6..bbb0fc57 100644
--- a/test/core/list/not.wren
+++ b/test/core/list/not.wren
@@ -1,2 +1,2 @@
-IO.print(![1, 2]) // expect: false
-IO.print(![])     // expect: false
+System.print(![1, 2]) // expect: false
+System.print(![])     // expect: false
diff --git a/test/core/list/plus.wren b/test/core/list/plus.wren
index d0dda410..98cf60ea 100644
--- a/test/core/list/plus.wren
+++ b/test/core/list/plus.wren
@@ -6,13 +6,13 @@ var e = a + []
 var f = [] + a
 var g = [] + []
 
-IO.print(a) // expect: [1, 2, 3]
-IO.print(b) // expect: [4, 5, 6]
-IO.print(c) // expect: [1, 2, 3, 4, 5, 6]
-IO.print(d) // expect: [1, 2, 3, 4, 5, 6]
-IO.print(e) // expect: [1, 2, 3]
-IO.print(f) // expect: [1, 2, 3]
-IO.print(g) // expect: []
+System.print(a) // expect: [1, 2, 3]
+System.print(b) // expect: [4, 5, 6]
+System.print(c) // expect: [1, 2, 3, 4, 5, 6]
+System.print(d) // expect: [1, 2, 3, 4, 5, 6]
+System.print(e) // expect: [1, 2, 3]
+System.print(f) // expect: [1, 2, 3]
+System.print(g) // expect: []
 
 // Doesn't modify original list.
-IO.print(a) // expect: [1, 2, 3]
+System.print(a) // expect: [1, 2, 3]
diff --git a/test/core/list/reduce.wren b/test/core/list/reduce.wren
index 87fb87ee..f2a92a8f 100644
--- a/test/core/list/reduce.wren
+++ b/test/core/list/reduce.wren
@@ -3,12 +3,12 @@ var b = ["W", "o", "r", "l", "d"]
 var max = Fn.new {|a, b| a > b ? a : b }
 var sum = Fn.new {|a, b| a + b }
 
-IO.print(a.reduce(max)) // expect: 5
-IO.print(a.reduce(10, max)) // expect: 10
+System.print(a.reduce(max)) // expect: 5
+System.print(a.reduce(10, max)) // expect: 10
 
-IO.print(a.reduce(sum)) // expect: 13
-IO.print(a.reduce(-1, sum)) // expect: 12
+System.print(a.reduce(sum)) // expect: 13
+System.print(a.reduce(-1, sum)) // expect: 12
 
 // sum also concatenates strings
-IO.print(b.reduce("Hello ", sum)) // expect: Hello World
-IO.print(b.reduce(sum)) // expect: World
+System.print(b.reduce("Hello ", sum)) // expect: Hello World
+System.print(b.reduce(sum)) // expect: World
diff --git a/test/core/list/reduce_single_item.wren b/test/core/list/reduce_single_item.wren
index 0f874c99..3ad5506c 100644
--- a/test/core/list/reduce_single_item.wren
+++ b/test/core/list/reduce_single_item.wren
@@ -1,2 +1,2 @@
-IO.print([1].reduce {|a, b| 42 }) // expect: 1
-IO.print([].reduce(1) {|a, b| 42 }) // expect: 1
+System.print([1].reduce {|a, b| 42 }) // expect: 1
+System.print([].reduce(1) {|a, b| 42 }) // expect: 1
diff --git a/test/core/list/remove_at.wren b/test/core/list/remove_at.wren
index 1668b20b..84f6b51b 100644
--- a/test/core/list/remove_at.wren
+++ b/test/core/list/remove_at.wren
@@ -1,27 +1,27 @@
 var a = [1, 2, 3]
 a.removeAt(0)
-IO.print(a) // expect: [2, 3]
+System.print(a) // expect: [2, 3]
 
 var b = [1, 2, 3]
 b.removeAt(1)
-IO.print(b) // expect: [1, 3]
+System.print(b) // expect: [1, 3]
 
 var c = [1, 2, 3]
 c.removeAt(2)
-IO.print(c) // expect: [1, 2]
+System.print(c) // expect: [1, 2]
 
 // Index backwards from end.
 var d = [1, 2, 3]
 d.removeAt(-3)
-IO.print(d) // expect: [2, 3]
+System.print(d) // expect: [2, 3]
 
 var e = [1, 2, 3]
 e.removeAt(-2)
-IO.print(e) // expect: [1, 3]
+System.print(e) // expect: [1, 3]
 
 var f = [1, 2, 3]
 f.removeAt(-1)
-IO.print(f) // expect: [1, 2]
+System.print(f) // expect: [1, 2]
 
 // Return the removed value.
-IO.print([3, 4, 5].removeAt(1)) // expect: 4
+System.print([3, 4, 5].removeAt(1)) // expect: 4
diff --git a/test/core/list/subscript.wren b/test/core/list/subscript.wren
index 8b38e3c3..19633013 100644
--- a/test/core/list/subscript.wren
+++ b/test/core/list/subscript.wren
@@ -1,12 +1,12 @@
 // Returns elements.
 var list = ["a", "b", "c", "d"]
-IO.print(list[0]) // expect: a
-IO.print(list[1]) // expect: b
-IO.print(list[2]) // expect: c
-IO.print(list[3]) // expect: d
+System.print(list[0]) // expect: a
+System.print(list[1]) // expect: b
+System.print(list[2]) // expect: c
+System.print(list[3]) // expect: d
 
 // Allows indexing backwards from the end.
-IO.print(list[-4]) // expect: a
-IO.print(list[-3]) // expect: b
-IO.print(list[-2]) // expect: c
-IO.print(list[-1]) // expect: d
+System.print(list[-4]) // expect: a
+System.print(list[-3]) // expect: b
+System.print(list[-2]) // expect: c
+System.print(list[-1]) // expect: d
diff --git a/test/core/list/subscript_range.wren b/test/core/list/subscript_range.wren
index 08a03a44..b22e9387 100644
--- a/test/core/list/subscript_range.wren
+++ b/test/core/list/subscript_range.wren
@@ -1,35 +1,35 @@
 // Returns lists.
 var list = ["a", "b", "c", "d", "e"]
-IO.print(list[0..0]) // expect: [a]
-IO.print(list[1...1]) // expect: []
-IO.print(list[1..2]) // expect: [b, c]
-IO.print(list[1...2]) // expect: [b]
-IO.print(list[2..4]) // expect: [c, d, e]
-IO.print(list[2...5]) // expect: [c, d, e]
+System.print(list[0..0]) // expect: [a]
+System.print(list[1...1]) // expect: []
+System.print(list[1..2]) // expect: [b, c]
+System.print(list[1...2]) // expect: [b]
+System.print(list[2..4]) // expect: [c, d, e]
+System.print(list[2...5]) // expect: [c, d, e]
 
 // A backwards range reverses.
-IO.print(list[3..1]) // expect: [d, c, b]
-IO.print(list[3...1]) // expect: [d, c]
-IO.print(list[3...3]) // expect: []
+System.print(list[3..1]) // expect: [d, c, b]
+System.print(list[3...1]) // expect: [d, c]
+System.print(list[3...3]) // expect: []
 
 // Negative ranges index from the end.
-IO.print(list[-5..-2]) // expect: [a, b, c, d]
-IO.print(list[-5...-2]) // expect: [a, b, c]
-IO.print(list[-3..-5]) // expect: [c, b, a]
-IO.print(list[-3...-6]) // expect: [c, b, a]
+System.print(list[-5..-2]) // expect: [a, b, c, d]
+System.print(list[-5...-2]) // expect: [a, b, c]
+System.print(list[-3..-5]) // expect: [c, b, a]
+System.print(list[-3...-6]) // expect: [c, b, a]
 
 // Half-negative ranges are treated like the negative value is fixed before
 // walking the range.
-IO.print(list[-5..3]) // expect: [a, b, c, d]
-IO.print(list[-3...5]) // expect: [c, d, e]
-IO.print(list[-2..1]) // expect: [d, c, b]
-IO.print(list[-2...0]) // expect: [d, c, b]
+System.print(list[-5..3]) // expect: [a, b, c, d]
+System.print(list[-3...5]) // expect: [c, d, e]
+System.print(list[-2..1]) // expect: [d, c, b]
+System.print(list[-2...0]) // expect: [d, c, b]
 
-IO.print(list[1..-2]) // expect: [b, c, d]
-IO.print(list[2...-1]) // expect: [c, d]
-IO.print(list[4..-5]) // expect: [e, d, c, b, a]
-IO.print(list[3...-6]) // expect: [d, c, b, a]
+System.print(list[1..-2]) // expect: [b, c, d]
+System.print(list[2...-1]) // expect: [c, d]
+System.print(list[4..-5]) // expect: [e, d, c, b, a]
+System.print(list[3...-6]) // expect: [d, c, b, a]
 
 // An empty range at zero is allowed on an empty list.
-IO.print([][0...0]) // expect: []
-IO.print([][0..-1]) // expect: []
+System.print([][0...0]) // expect: []
+System.print([][0..-1]) // expect: []
diff --git a/test/core/list/subscript_setter.wren b/test/core/list/subscript_setter.wren
index 02d56fb3..2de12da3 100644
--- a/test/core/list/subscript_setter.wren
+++ b/test/core/list/subscript_setter.wren
@@ -4,13 +4,13 @@
   list[0] = 5
   list[1] = 6
   list[2] = 7
-  IO.print(list) // expect: [5, 6, 7]
+  System.print(list) // expect: [5, 6, 7]
 }
 
 // Returns right-hand side.
 {
   var list = [1, 2, 3]
-  IO.print(list[1] = 5) // expect: 5
+  System.print(list[1] = 5) // expect: 5
 }
 
 // Negative indices.
@@ -19,5 +19,5 @@
   list[-1] = 5
   list[-2] = 6
   list[-3] = 7
-  IO.print(list) // expect: [7, 6, 5]
+  System.print(list) // expect: [7, 6, 5]
 }
diff --git a/test/core/list/to_string.wren b/test/core/list/to_string.wren
index 8392aa96..d5a23b98 100644
--- a/test/core/list/to_string.wren
+++ b/test/core/list/to_string.wren
@@ -1,11 +1,11 @@
 // Handle empty list.
-IO.print([].toString)             // expect: []
+System.print([].toString)             // expect: []
 
 // Does not quote strings.
-IO.print([1, "2", true].toString) // expect: [1, 2, true]
+System.print([1, "2", true].toString) // expect: [1, 2, true]
 
 // Nested lists.
-IO.print([1, [2, [3], 4], 5]) // expect: [1, [2, [3], 4], 5]
+System.print([1, [2, [3], 4], 5]) // expect: [1, [2, [3], 4], 5]
 
 // Calls toString on elements.
 class Foo {
@@ -13,6 +13,6 @@ class Foo {
   toString { "Foo.toString" }
 }
 
-IO.print([1, Foo.new(), 2]) // expect: [1, Foo.toString, 2]
+System.print([1, Foo.new(), 2]) // expect: [1, Foo.toString, 2]
 
 // TODO: Handle lists that contain themselves.
diff --git a/test/core/list/type.wren b/test/core/list/type.wren
index 19f706dc..983ac4f8 100644
--- a/test/core/list/type.wren
+++ b/test/core/list/type.wren
@@ -1,5 +1,5 @@
-IO.print([] is List)      // expect: true
-IO.print([] is Sequence)  // expect: true
-IO.print([] is Object)    // expect: true
-IO.print([] is Bool)      // expect: false
-IO.print([].type == List) // expect: true
+System.print([] is List)      // expect: true
+System.print([] is Sequence)  // expect: true
+System.print([] is Object)    // expect: true
+System.print([] is Bool)      // expect: false
+System.print([].type == List) // expect: true
diff --git a/test/core/list/where.wren b/test/core/list/where.wren
index 24383d4f..6a92f39f 100644
--- a/test/core/list/where.wren
+++ b/test/core/list/where.wren
@@ -1,6 +1,6 @@
 var a = [1, 2, 3]
 var b = a.where {|x| x > 1 }.toList
-IO.print(b) // expect: [2, 3]
+System.print(b) // expect: [2, 3]
 
 var c = a.where {|x| x > 10 }.toList
-IO.print(c) // expect: []
+System.print(c) // expect: []
diff --git a/test/core/map/churn.wren b/test/core/map/churn.wren
index 97674638..0019011b 100644
--- a/test/core/map/churn.wren
+++ b/test/core/map/churn.wren
@@ -8,4 +8,4 @@ for (i in 0...100) {
   if (i >= 10) map.remove(i - 10)
 }
 
-IO.print(map.count) // expect: 10
+System.print(map.count) // expect: 10
diff --git a/test/core/map/clear.wren b/test/core/map/clear.wren
index a580af89..e4b488f5 100644
--- a/test/core/map/clear.wren
+++ b/test/core/map/clear.wren
@@ -1,7 +1,7 @@
 var a = {1: 1, 2: 2, 3: 3}
 a.clear()
-IO.print(a)       // expect: {}
-IO.print(a.count) // expect: 0
+System.print(a)       // expect: {}
+System.print(a.count) // expect: 0
 
 // Returns null.
-IO.print({1: 2}.clear()) // expect: null
+System.print({1: 2}.clear()) // expect: null
diff --git a/test/core/map/contains_key.wren b/test/core/map/contains_key.wren
index 9dc97c23..298b30bc 100644
--- a/test/core/map/contains_key.wren
+++ b/test/core/map/contains_key.wren
@@ -4,8 +4,8 @@ var map = {
   "three": 3
 }
 
-IO.print(map.containsKey("one")) // expect: true
-IO.print(map.containsKey("two")) // expect: true
-IO.print(map.containsKey("three")) // expect: true
-IO.print(map.containsKey("four")) // expect: false
-IO.print(map.containsKey("five")) // expect: false
+System.print(map.containsKey("one")) // expect: true
+System.print(map.containsKey("two")) // expect: true
+System.print(map.containsKey("three")) // expect: true
+System.print(map.containsKey("four")) // expect: false
+System.print(map.containsKey("five")) // expect: false
diff --git a/test/core/map/count.wren b/test/core/map/count.wren
index 028258fe..59fb07a2 100644
--- a/test/core/map/count.wren
+++ b/test/core/map/count.wren
@@ -1,12 +1,12 @@
 var map = {}
-IO.print(map.count) // expect: 0
+System.print(map.count) // expect: 0
 map["one"] = "value"
-IO.print(map.count) // expect: 1
+System.print(map.count) // expect: 1
 map["two"] = "value"
-IO.print(map.count) // expect: 2
+System.print(map.count) // expect: 2
 map["three"] = "value"
-IO.print(map.count) // expect: 3
+System.print(map.count) // expect: 3
 
 // Adding existing key does not increase count.
 map["two"] = "new value"
-IO.print(map.count) // expect: 3
+System.print(map.count) // expect: 3
diff --git a/test/core/map/empty_string_key.wren b/test/core/map/empty_string_key.wren
index 9af72953..64b9e0f2 100644
--- a/test/core/map/empty_string_key.wren
+++ b/test/core/map/empty_string_key.wren
@@ -2,4 +2,4 @@ var map = {
   "": "empty string"
 }
 
-IO.print(map[""]) // expect: empty string
+System.print(map[""]) // expect: empty string
diff --git a/test/core/map/key_iterate.wren b/test/core/map/key_iterate.wren
index f1b169a0..7a111358 100644
--- a/test/core/map/key_iterate.wren
+++ b/test/core/map/key_iterate.wren
@@ -4,23 +4,23 @@ var a = {"one": 1, "two": 2, "three": 3, "four": 4}.keys
 // entry table and the hashing process isn't specified. So we just validate
 // what we can assume about them.
 
-IO.print(a.iterate(null) is Num) // expect: true
-IO.print(a.iterate(null) >= 0) // expect: true
+System.print(a.iterate(null) is Num) // expect: true
+System.print(a.iterate(null) >= 0) // expect: true
 
-IO.print(a.iterate(0) is Num) // expect: true
-IO.print(a.iterate(0) > 0) // expect: true
-IO.print(a.iterate(1) is Num) // expect: true
-IO.print(a.iterate(1) > 0) // expect: true
-IO.print(a.iterate(2) is Num) // expect: true
-IO.print(a.iterate(2) > 0) // expect: true
-IO.print(a.iterate(3) is Num) // expect: true
-IO.print(a.iterate(3) > 0) // expect: true
+System.print(a.iterate(0) is Num) // expect: true
+System.print(a.iterate(0) > 0) // expect: true
+System.print(a.iterate(1) is Num) // expect: true
+System.print(a.iterate(1) > 0) // expect: true
+System.print(a.iterate(2) is Num) // expect: true
+System.print(a.iterate(2) > 0) // expect: true
+System.print(a.iterate(3) is Num) // expect: true
+System.print(a.iterate(3) > 0) // expect: true
 
 var previous = -1
 var iterator = a.iterate(null)
 while (iterator) {
-  IO.print(iterator > previous)
-  IO.print(iterator is Num)
+  System.print(iterator > previous)
+  System.print(iterator is Num)
   previous = iterator
   iterator = a.iterate(iterator)
 }
@@ -38,8 +38,8 @@ while (iterator) {
 // expect: true
 
 // Out of bounds.
-IO.print(a.iterate(16)) // expect: false
-IO.print(a.iterate(-1)) // expect: false
+System.print(a.iterate(16)) // expect: false
+System.print(a.iterate(-1)) // expect: false
 
 // Nothing to iterate in an empty map.
-IO.print({}.keys.iterate(null)) // expect: false
+System.print({}.keys.iterate(null)) // expect: false
diff --git a/test/core/map/key_types.wren b/test/core/map/key_types.wren
index 57ec3519..e6ec71dc 100644
--- a/test/core/map/key_types.wren
+++ b/test/core/map/key_types.wren
@@ -12,17 +12,17 @@ var map = {
   fiber: "fiber"
 }
 
-IO.print(map[null]) // expect: null value
-IO.print(map[true]) // expect: true value
-IO.print(map[false]) // expect: false value
-IO.print(map[0]) // expect: zero
-IO.print(map[1.2]) // expect: 1 point 2
-IO.print(map[List]) // expect: list class
-IO.print(map["null"]) // expect: string value
-IO.print(map[1..3]) // expect: 1 to 3
-IO.print(map[fiber]) // expect: fiber
+System.print(map[null]) // expect: null value
+System.print(map[true]) // expect: true value
+System.print(map[false]) // expect: false value
+System.print(map[0]) // expect: zero
+System.print(map[1.2]) // expect: 1 point 2
+System.print(map[List]) // expect: list class
+System.print(map["null"]) // expect: string value
+System.print(map[1..3]) // expect: 1 to 3
+System.print(map[fiber]) // expect: fiber
 
-IO.print(map.count) // expect: 9
+System.print(map.count) // expect: 9
 
 // Use the same keys (but sometimes different objects) to ensure keys have the
 // right equality semantics.
@@ -35,13 +35,13 @@ map[[].type] = "new list class"
 map["nu" + "ll"] = "new string value"
 map[(3 - 2)..(1 + 2)] = "new 1 to 3"
 
-IO.print(map[null]) // expect: new null value
-IO.print(map[true]) // expect: new true value
-IO.print(map[false]) // expect: new false value
-IO.print(map[0]) // expect: new zero
-IO.print(map[1.2]) // expect: new 1 point 2
-IO.print(map[List]) // expect: new list class
-IO.print(map["null"]) // expect: new string value
-IO.print(map[1..3]) // expect: new 1 to 3
+System.print(map[null]) // expect: new null value
+System.print(map[true]) // expect: new true value
+System.print(map[false]) // expect: new false value
+System.print(map[0]) // expect: new zero
+System.print(map[1.2]) // expect: new 1 point 2
+System.print(map[List]) // expect: new list class
+System.print(map["null"]) // expect: new string value
+System.print(map[1..3]) // expect: new 1 to 3
 
-IO.print(map.count) // expect: 9
+System.print(map.count) // expect: 9
diff --git a/test/core/map/new.wren b/test/core/map/new.wren
index 557ee40c..1f917078 100644
--- a/test/core/map/new.wren
+++ b/test/core/map/new.wren
@@ -1,4 +1,4 @@
 var map = Map.new()
 
-IO.print(map.count) // expect: 0
-IO.print(map) // expect: {}
+System.print(map.count) // expect: 0
+System.print(map) // expect: {}
diff --git a/test/core/map/remove.wren b/test/core/map/remove.wren
index ce5a9d4d..53bff7c4 100644
--- a/test/core/map/remove.wren
+++ b/test/core/map/remove.wren
@@ -4,15 +4,15 @@ var map = {
   "three": 3
 }
 
-IO.print(map.count) // expect: 3
-IO.print(map.remove("two")) // expect: 2
-IO.print(map.count) // expect: 2
-IO.print(map.remove("three")) // expect: 3
-IO.print(map.count) // expect: 1
+System.print(map.count) // expect: 3
+System.print(map.remove("two")) // expect: 2
+System.print(map.count) // expect: 2
+System.print(map.remove("three")) // expect: 3
+System.print(map.count) // expect: 1
 
 // Remove an already removed entry.
-IO.print(map.remove("two")) // expect: null
-IO.print(map.count) // expect: 1
+System.print(map.remove("two")) // expect: null
+System.print(map.count) // expect: 1
 
-IO.print(map.remove("one")) // expect: 1
-IO.print(map.count) // expect: 0
+System.print(map.remove("one")) // expect: 1
+System.print(map.count) // expect: 0
diff --git a/test/core/map/subscript_empty_map.wren b/test/core/map/subscript_empty_map.wren
index bd453aae..05ee6680 100644
--- a/test/core/map/subscript_empty_map.wren
+++ b/test/core/map/subscript_empty_map.wren
@@ -1,4 +1,4 @@
 // This is a regression test to ensure map handles a null entry array.
 
 var map = {}
-IO.print(map["key"]) // expect: null
+System.print(map["key"]) // expect: null
diff --git a/test/core/map/to_string.wren b/test/core/map/to_string.wren
index 66a951b4..370d3979 100644
--- a/test/core/map/to_string.wren
+++ b/test/core/map/to_string.wren
@@ -1,11 +1,11 @@
 // Handle empty map.
-IO.print({}.toString)             // expect: {}
+System.print({}.toString)             // expect: {}
 
 // Does not quote strings.
-IO.print({"1": "2"}.toString) // expect: {1: 2}
+System.print({"1": "2"}.toString) // expect: {1: 2}
 
 // Nested maps.
-IO.print({1: {2: {}}}) // expect: {1: {2: {}}}
+System.print({1: {2: {}}}) // expect: {1: {2: {}}}
 
 // Calls toString on elements.
 class Foo {
@@ -13,12 +13,12 @@ class Foo {
   toString { "Foo.toString" }
 }
 
-IO.print({1: Foo.new()}) // expect: {1: Foo.toString}
+System.print({1: Foo.new()}) // expect: {1: Foo.toString}
 
 // Since iteration order is unspecified, we don't know what order the results
 // will be.
 var s = {1: 2, 3: 4, 5: 6}.toString
-IO.print(s == "{1: 2, 3: 4, 5: 6}" ||
+System.print(s == "{1: 2, 3: 4, 5: 6}" ||
          s == "{1: 2, 5: 6, 3: 4}" ||
          s == "{3: 4, 1: 2, 5: 6}" ||
          s == "{3: 4, 5: 6, 1: 2}" ||
diff --git a/test/core/map/type.wren b/test/core/map/type.wren
index 11e4913b..63507b32 100644
--- a/test/core/map/type.wren
+++ b/test/core/map/type.wren
@@ -1,5 +1,5 @@
-IO.print({} is Map)      // expect: true
+System.print({} is Map)      // expect: true
 // TODO: Abstract base class for associations.
-IO.print({} is Object)    // expect: true
-IO.print({} is Bool)      // expect: false
-IO.print({}.type == Map) // expect: true
+System.print({} is Object)    // expect: true
+System.print({} is Bool)      // expect: false
+System.print({}.type == Map) // expect: true
diff --git a/test/core/map/value_iterate.wren b/test/core/map/value_iterate.wren
index cf185abf..7026164e 100644
--- a/test/core/map/value_iterate.wren
+++ b/test/core/map/value_iterate.wren
@@ -4,23 +4,23 @@ var a = {"one": 1, "two": 2, "three": 3, "four": 4}.values
 // entry table and the hashing process isn't specified. So we just validate
 // what we can assume about them.
 
-IO.print(a.iterate(null) is Num) // expect: true
-IO.print(a.iterate(null) >= 0) // expect: true
+System.print(a.iterate(null) is Num) // expect: true
+System.print(a.iterate(null) >= 0) // expect: true
 
-IO.print(a.iterate(0) is Num) // expect: true
-IO.print(a.iterate(0) > 0) // expect: true
-IO.print(a.iterate(1) is Num) // expect: true
-IO.print(a.iterate(1) > 0) // expect: true
-IO.print(a.iterate(2) is Num) // expect: true
-IO.print(a.iterate(2) > 0) // expect: true
-IO.print(a.iterate(3) is Num) // expect: true
-IO.print(a.iterate(3) > 0) // expect: true
+System.print(a.iterate(0) is Num) // expect: true
+System.print(a.iterate(0) > 0) // expect: true
+System.print(a.iterate(1) is Num) // expect: true
+System.print(a.iterate(1) > 0) // expect: true
+System.print(a.iterate(2) is Num) // expect: true
+System.print(a.iterate(2) > 0) // expect: true
+System.print(a.iterate(3) is Num) // expect: true
+System.print(a.iterate(3) > 0) // expect: true
 
 var previous = -1
 var iterator = a.iterate(null)
 while (iterator) {
-  IO.print(iterator > previous)
-  IO.print(iterator is Num)
+  System.print(iterator > previous)
+  System.print(iterator is Num)
   previous = iterator
   iterator = a.iterate(iterator)
 }
@@ -38,8 +38,8 @@ while (iterator) {
 // expect: true
 
 // Out of bounds.
-IO.print(a.iterate(16)) // expect: false
-IO.print(a.iterate(-1)) // expect: false
+System.print(a.iterate(16)) // expect: false
+System.print(a.iterate(-1)) // expect: false
 
 // Nothing to iterate in an empty map.
-IO.print({}.values.iterate(null)) // expect: false
+System.print({}.values.iterate(null)) // expect: false
diff --git a/test/core/null/not.wren b/test/core/null/not.wren
index 630200d3..6219e0ec 100644
--- a/test/core/null/not.wren
+++ b/test/core/null/not.wren
@@ -1 +1 @@
-IO.print(!null) // expect: true
+System.print(!null) // expect: true
diff --git a/test/core/null/type.wren b/test/core/null/type.wren
index 3fdb2628..64c2781c 100644
--- a/test/core/null/type.wren
+++ b/test/core/null/type.wren
@@ -1,4 +1,4 @@
-IO.print(null is Null)      // expect: true
-IO.print(null is Object)    // expect: true
-IO.print(null is Bool)      // expect: false
-IO.print(null.type == Null) // expect: true
+System.print(null is Null)      // expect: true
+System.print(null is Object)    // expect: true
+System.print(null is Bool)      // expect: false
+System.print(null.type == Null) // expect: true
diff --git a/test/core/number/abs.wren b/test/core/number/abs.wren
index 171b3ebb..eb4a4777 100644
--- a/test/core/number/abs.wren
+++ b/test/core/number/abs.wren
@@ -1,6 +1,6 @@
-IO.print(123.abs)      // expect: 123
-IO.print((-123).abs)   // expect: 123
-IO.print(0.abs)        // expect: 0
-IO.print((-0).abs)     // expect: 0
-IO.print((-0.12).abs)  // expect: 0.12
-IO.print(12.34.abs)    // expect: 12.34
+System.print(123.abs)      // expect: 123
+System.print((-123).abs)   // expect: 123
+System.print(0.abs)        // expect: 0
+System.print((-0).abs)     // expect: 0
+System.print((-0.12).abs)  // expect: 0.12
+System.print(12.34.abs)    // expect: 12.34
diff --git a/test/core/number/acos.wren b/test/core/number/acos.wren
index 54d54da9..94138b18 100644
--- a/test/core/number/acos.wren
+++ b/test/core/number/acos.wren
@@ -1,3 +1,3 @@
-IO.print(0.acos)        // expect: 1.5707963267949
-IO.print(1.acos)        // expect: 0
-IO.print((-1).acos)     // expect: 3.1415926535898
+System.print(0.acos)        // expect: 1.5707963267949
+System.print(1.acos)        // expect: 0
+System.print((-1).acos)     // expect: 3.1415926535898
diff --git a/test/core/number/asin.wren b/test/core/number/asin.wren
index e6c312af..bf6be347 100644
--- a/test/core/number/asin.wren
+++ b/test/core/number/asin.wren
@@ -1,3 +1,3 @@
-IO.print(0.asin)        // expect: 0
-IO.print(1.asin)        // expect: 1.5707963267949
-IO.print((-1).asin)     // expect: -1.5707963267949
+System.print(0.asin)        // expect: 0
+System.print(1.asin)        // expect: 1.5707963267949
+System.print((-1).asin)     // expect: -1.5707963267949
diff --git a/test/core/number/atan.wren b/test/core/number/atan.wren
index 822315d7..89445907 100644
--- a/test/core/number/atan.wren
+++ b/test/core/number/atan.wren
@@ -1,2 +1,2 @@
-IO.print(0.atan)        // expect: 0
-IO.print(1.atan)        // expect: 0.78539816339745
+System.print(0.atan)        // expect: 0
+System.print(1.atan)        // expect: 0.78539816339745
diff --git a/test/core/number/atan2.wren b/test/core/number/atan2.wren
index e1f5289f..d9354cbf 100644
--- a/test/core/number/atan2.wren
+++ b/test/core/number/atan2.wren
@@ -1,4 +1,4 @@
-IO.print(0.atan(0))     // expect: 0
-IO.print(0.atan(1))     // expect: 0
+System.print(0.atan(0))     // expect: 0
+System.print(0.atan(1))     // expect: 0
 
-IO.print(1.atan(0))     // expect: 1.5707963267949
+System.print(1.atan(0))     // expect: 1.5707963267949
diff --git a/test/core/number/bitwise_and.wren b/test/core/number/bitwise_and.wren
index c63ff382..4199ba17 100644
--- a/test/core/number/bitwise_and.wren
+++ b/test/core/number/bitwise_and.wren
@@ -1,12 +1,12 @@
-IO.print(0 & 0) // expect: 0
-IO.print(2863311530 & 1431655765) // expect: 0
-IO.print(4042322160 & 1010580540) // expect: 808464432
+System.print(0 & 0) // expect: 0
+System.print(2863311530 & 1431655765) // expect: 0
+System.print(4042322160 & 1010580540) // expect: 808464432
 
 // Max u32 value.
-IO.print(4294967295 & 4294967295) // expect: 4294967295
+System.print(4294967295 & 4294967295) // expect: 4294967295
 
 // Past max u32 value.
-IO.print(4294967296 & 4294967296) // expect: 0
+System.print(4294967296 & 4294967296) // expect: 0
 
 // TODO: Negative numbers.
 // TODO: Floating-point numbers.
diff --git a/test/core/number/bitwise_lsh.wren b/test/core/number/bitwise_lsh.wren
index 28d1e74d..8252b813 100644
--- a/test/core/number/bitwise_lsh.wren
+++ b/test/core/number/bitwise_lsh.wren
@@ -1,15 +1,15 @@
-IO.print(0 << 0) // expect: 0
-IO.print(1 << 0) // expect: 1
-IO.print(0 << 1) // expect: 0
-IO.print(1 << 1) // expect: 2
-IO.print(2863311530 << 1) // expect: 1431655764
-IO.print(4042322160 << 1) // expect: 3789677024
+System.print(0 << 0) // expect: 0
+System.print(1 << 0) // expect: 1
+System.print(0 << 1) // expect: 0
+System.print(1 << 1) // expect: 2
+System.print(2863311530 << 1) // expect: 1431655764
+System.print(4042322160 << 1) // expect: 3789677024
 
 // Max u32 value.
-IO.print(4294967295 << 1) // expect: 4294967294
+System.print(4294967295 << 1) // expect: 4294967294
 
 // Past max u32 value.
-IO.print(4294967296 << 1) // expect: 0
+System.print(4294967296 << 1) // expect: 0
 
 // TODO: Negative numbers.
 // TODO: Floating-point numbers.
diff --git a/test/core/number/bitwise_not.wren b/test/core/number/bitwise_not.wren
index 06676c4a..9c1f5b36 100644
--- a/test/core/number/bitwise_not.wren
+++ b/test/core/number/bitwise_not.wren
@@ -1,22 +1,22 @@
-IO.print(~0) // expect: 4294967295
-IO.print(~1) // expect: 4294967294
-IO.print(~23) // expect: 4294967272
+System.print(~0) // expect: 4294967295
+System.print(~1) // expect: 4294967294
+System.print(~23) // expect: 4294967272
 
 // Max u32 value.
-IO.print(~4294967295) // expect: 0
+System.print(~4294967295) // expect: 0
 
 // Past max u32 value.
-IO.print(~4294967296) // expect: 4294967295
+System.print(~4294967296) // expect: 4294967295
 
 // Negative numbers.
-IO.print(~-1) // expect: 0
-IO.print(~-123) // expect: 122
-IO.print(~-4294967294) // expect: 4294967293
-IO.print(~-4294967295) // expect: 4294967294
-IO.print(~-4294967296) // expect: 4294967295
+System.print(~-1) // expect: 0
+System.print(~-123) // expect: 122
+System.print(~-4294967294) // expect: 4294967293
+System.print(~-4294967295) // expect: 4294967294
+System.print(~-4294967296) // expect: 4294967295
 
 // Floating point values.
-IO.print(~1.23) // expect: 4294967294
-IO.print(~0.00123) // expect: 4294967295
-IO.print(~345.67) // expect: 4294966950
-IO.print(~-12.34) // expect: 11
+System.print(~1.23) // expect: 4294967294
+System.print(~0.00123) // expect: 4294967295
+System.print(~345.67) // expect: 4294966950
+System.print(~-12.34) // expect: 11
diff --git a/test/core/number/bitwise_or.wren b/test/core/number/bitwise_or.wren
index 6cf75cdb..5fe087ab 100644
--- a/test/core/number/bitwise_or.wren
+++ b/test/core/number/bitwise_or.wren
@@ -1,12 +1,12 @@
-IO.print(0 | 0) // expect: 0
-IO.print(2863311530 | 1431655765) // expect: 4294967295
-IO.print(3435973836 | 1717986918) // expect: 4008636142
+System.print(0 | 0) // expect: 0
+System.print(2863311530 | 1431655765) // expect: 4294967295
+System.print(3435973836 | 1717986918) // expect: 4008636142
 
 // Max u32 value.
-IO.print(4294967295 | 4294967295) // expect: 4294967295
+System.print(4294967295 | 4294967295) // expect: 4294967295
 
 // Past max u32 value.
-IO.print(4294967296 | 4294967296) // expect: 0
+System.print(4294967296 | 4294967296) // expect: 0
 
 // TODO: Negative numbers.
 // TODO: Floating-point numbers.
diff --git a/test/core/number/bitwise_rsh.wren b/test/core/number/bitwise_rsh.wren
index 18c5892d..57beaf83 100644
--- a/test/core/number/bitwise_rsh.wren
+++ b/test/core/number/bitwise_rsh.wren
@@ -1,15 +1,15 @@
-IO.print(0 >> 0) // expect: 0
-IO.print(1 >> 0) // expect: 1
-IO.print(0 >> 1) // expect: 0
-IO.print(1 >> 1) // expect: 0
-IO.print(2863311530 >> 1) // expect: 1431655765
-IO.print(4042322160 >> 1) // expect: 2021161080
+System.print(0 >> 0) // expect: 0
+System.print(1 >> 0) // expect: 1
+System.print(0 >> 1) // expect: 0
+System.print(1 >> 1) // expect: 0
+System.print(2863311530 >> 1) // expect: 1431655765
+System.print(4042322160 >> 1) // expect: 2021161080
 
 // Max u32 value.
-IO.print(4294967295 >> 1) // expect: 2147483647
+System.print(4294967295 >> 1) // expect: 2147483647
 
 // Past max u32 value.
-IO.print(4294967296 >> 1) // expect: 0
+System.print(4294967296 >> 1) // expect: 0
 
 // TODO: Negative numbers.
 // TODO: Floating-point numbers.
diff --git a/test/core/number/bitwise_xor.wren b/test/core/number/bitwise_xor.wren
index 49530eda..039d4132 100644
--- a/test/core/number/bitwise_xor.wren
+++ b/test/core/number/bitwise_xor.wren
@@ -1,15 +1,15 @@
-IO.print(0 ^ 0) // expect: 0
-IO.print(1 ^ 1) // expect: 0
-IO.print(0 ^ 1) // expect: 1
-IO.print(1 ^ 0) // expect: 1
-IO.print(2863311530 ^ 1431655765) // expect: 4294967295
-IO.print(4042322160 ^ 1010580540) // expect: 3435973836
+System.print(0 ^ 0) // expect: 0
+System.print(1 ^ 1) // expect: 0
+System.print(0 ^ 1) // expect: 1
+System.print(1 ^ 0) // expect: 1
+System.print(2863311530 ^ 1431655765) // expect: 4294967295
+System.print(4042322160 ^ 1010580540) // expect: 3435973836
 
 // Max u32 value.
-IO.print(4294967295 ^ 4294967295) // expect: 0
+System.print(4294967295 ^ 4294967295) // expect: 0
 
 // Past max u32 value.
-IO.print(4294967296 ^ 4294967296) // expect: 0
+System.print(4294967296 ^ 4294967296) // expect: 0
 
 // TODO: Negative numbers.
 // TODO: Floating-point numbers.
diff --git a/test/core/number/ceil.wren b/test/core/number/ceil.wren
index fe510dbd..6bddecee 100644
--- a/test/core/number/ceil.wren
+++ b/test/core/number/ceil.wren
@@ -1,8 +1,8 @@
-IO.print(123.ceil)      // expect: 123
-IO.print((-123).ceil)   // expect: -123
-IO.print(0.ceil)        // expect: 0
-IO.print((-0).ceil)     // expect: -0
-IO.print(0.123.ceil)    // expect: 1
-IO.print(12.3.ceil)     // expect: 13
-IO.print((-0.123).ceil) // expect: -0
-IO.print((-12.3).ceil)  // expect: -12
+System.print(123.ceil)      // expect: 123
+System.print((-123).ceil)   // expect: -123
+System.print(0.ceil)        // expect: 0
+System.print((-0).ceil)     // expect: -0
+System.print(0.123.ceil)    // expect: 1
+System.print(12.3.ceil)     // expect: 13
+System.print((-0.123).ceil) // expect: -0
+System.print((-12.3).ceil)  // expect: -12
diff --git a/test/core/number/comparison.wren b/test/core/number/comparison.wren
index 8cee6c47..c71bf11d 100644
--- a/test/core/number/comparison.wren
+++ b/test/core/number/comparison.wren
@@ -1,27 +1,27 @@
-IO.print(1 < 2)    // expect: true
-IO.print(2 < 2)    // expect: false
-IO.print(2 < 1)    // expect: false
+System.print(1 < 2)    // expect: true
+System.print(2 < 2)    // expect: false
+System.print(2 < 1)    // expect: false
 
-IO.print(1 <= 2)    // expect: true
-IO.print(2 <= 2)    // expect: true
-IO.print(2 <= 1)    // expect: false
+System.print(1 <= 2)    // expect: true
+System.print(2 <= 2)    // expect: true
+System.print(2 <= 1)    // expect: false
 
-IO.print(1 > 2)    // expect: false
-IO.print(2 > 2)    // expect: false
-IO.print(2 > 1)    // expect: true
+System.print(1 > 2)    // expect: false
+System.print(2 > 2)    // expect: false
+System.print(2 > 1)    // expect: true
 
-IO.print(1 >= 2)    // expect: false
-IO.print(2 >= 2)    // expect: true
-IO.print(2 >= 1)    // expect: true
+System.print(1 >= 2)    // expect: false
+System.print(2 >= 2)    // expect: true
+System.print(2 >= 1)    // expect: true
 
 // Zero and negative zero compare the same.
-IO.print(0 < -0) // expect: false
-IO.print(-0 < 0) // expect: false
-IO.print(0 > -0) // expect: false
-IO.print(-0 > 0) // expect: false
-IO.print(0 <= -0) // expect: true
-IO.print(-0 <= 0) // expect: true
-IO.print(0 >= -0) // expect: true
-IO.print(-0 >= 0) // expect: true
+System.print(0 < -0) // expect: false
+System.print(-0 < 0) // expect: false
+System.print(0 > -0) // expect: false
+System.print(-0 > 0) // expect: false
+System.print(0 <= -0) // expect: true
+System.print(-0 <= 0) // expect: true
+System.print(0 >= -0) // expect: true
+System.print(-0 >= 0) // expect: true
 
 // TODO: Wrong type for RHS.
diff --git a/test/core/number/cos.wren b/test/core/number/cos.wren
index b7be49af..b7672271 100644
--- a/test/core/number/cos.wren
+++ b/test/core/number/cos.wren
@@ -1,6 +1,6 @@
-IO.print(0.cos)             // expect: 1
-IO.print(Num.pi.cos)        // expect: -1
-IO.print((2 * Num.pi).cos)  // expect: 1
+System.print(0.cos)             // expect: 1
+System.print(Num.pi.cos)        // expect: -1
+System.print((2 * Num.pi).cos)  // expect: 1
 
 // this should of course be 0, but it's not that precise
-IO.print((Num.pi / 2).cos)  // expect: 6.1232339957368e-17
+System.print((Num.pi / 2).cos)  // expect: 6.1232339957368e-17
diff --git a/test/core/number/divide.wren b/test/core/number/divide.wren
index 85aef751..5a3966a6 100644
--- a/test/core/number/divide.wren
+++ b/test/core/number/divide.wren
@@ -1,12 +1,12 @@
-IO.print(8 / 2)         // expect: 4
-IO.print(12.34 / -0.4)  // expect: -30.85
+System.print(8 / 2)         // expect: 4
+System.print(12.34 / -0.4)  // expect: -30.85
 
 // Divide by zero.
-IO.print(3 / 0)         // expect: infinity
-IO.print(-3 / 0)        // expect: -infinity
-IO.print(0 / 0)         // expect: nan
-IO.print(-0 / 0)        // expect: nan
-IO.print(3 / -0)        // expect: -infinity
-IO.print(-3 / -0)       // expect: infinity
-IO.print(0 / -0)        // expect: nan
-IO.print(-0 / -0)       // expect: nan
+System.print(3 / 0)         // expect: infinity
+System.print(-3 / 0)        // expect: -infinity
+System.print(0 / 0)         // expect: nan
+System.print(-0 / 0)        // expect: nan
+System.print(3 / -0)        // expect: -infinity
+System.print(-3 / -0)       // expect: infinity
+System.print(0 / -0)        // expect: nan
+System.print(-0 / -0)       // expect: nan
diff --git a/test/core/number/equality.wren b/test/core/number/equality.wren
index 9b777037..ee7e29c7 100644
--- a/test/core/number/equality.wren
+++ b/test/core/number/equality.wren
@@ -1,19 +1,19 @@
-IO.print(123 == 123)  // expect: true
-IO.print(123 == 124)  // expect: false
-IO.print(-3 == 3)     // expect: false
-IO.print(0 == -0)     // expect: true
+System.print(123 == 123)  // expect: true
+System.print(123 == 124)  // expect: false
+System.print(-3 == 3)     // expect: false
+System.print(0 == -0)     // expect: true
 
 // Not equal to other types.
-IO.print(123 == "123") // expect: false
-IO.print(1 == true)    // expect: false
-IO.print(0 == false)   // expect: false
+System.print(123 == "123") // expect: false
+System.print(1 == true)    // expect: false
+System.print(0 == false)   // expect: false
 
-IO.print(123 != 123)  // expect: false
-IO.print(123 != 124)  // expect: true
-IO.print(-3 != 3)     // expect: true
-IO.print(0 != -0)     // expect: false
+System.print(123 != 123)  // expect: false
+System.print(123 != 124)  // expect: true
+System.print(-3 != 3)     // expect: true
+System.print(0 != -0)     // expect: false
 
 // Not equal to other types.
-IO.print(123 != "123") // expect: true
-IO.print(1 != true)    // expect: true
-IO.print(0 != false)   // expect: true
+System.print(123 != "123") // expect: true
+System.print(1 != true)    // expect: true
+System.print(0 != false)   // expect: true
diff --git a/test/core/number/floor.wren b/test/core/number/floor.wren
index 063f0361..985809f4 100644
--- a/test/core/number/floor.wren
+++ b/test/core/number/floor.wren
@@ -1,8 +1,8 @@
-IO.print(123.floor)      // expect: 123
-IO.print((-123).floor)   // expect: -123
-IO.print(0.floor)        // expect: 0
-IO.print((-0).floor)     // expect: -0
-IO.print(0.123.floor)    // expect: 0
-IO.print(12.3.floor)     // expect: 12
-IO.print((-0.123).floor) // expect: -1
-IO.print((-12.3).floor)  // expect: -13
+System.print(123.floor)      // expect: 123
+System.print((-123).floor)   // expect: -123
+System.print(0.floor)        // expect: 0
+System.print((-0).floor)     // expect: -0
+System.print(0.123.floor)    // expect: 0
+System.print(12.3.floor)     // expect: 12
+System.print((-0.123).floor) // expect: -1
+System.print((-12.3).floor)  // expect: -13
diff --git a/test/core/number/fraction.wren b/test/core/number/fraction.wren
index 33be0dea..9af87ce5 100644
--- a/test/core/number/fraction.wren
+++ b/test/core/number/fraction.wren
@@ -1,19 +1,19 @@
-IO.print(123.fraction)      // expect: 0
-IO.print((-123).fraction)   // expect: -0
-IO.print(0.fraction)        // expect: 0
-IO.print((-0).fraction)     // expect: -0
-IO.print(0.123.fraction)    // expect: 0.123
-IO.print(12.3.fraction)     // expect: 0.3
-IO.print((-0.123).fraction) // expect: -0.123
-IO.print((-12.3).fraction)  // expect: -0.3
+System.print(123.fraction)      // expect: 0
+System.print((-123).fraction)   // expect: -0
+System.print(0.fraction)        // expect: 0
+System.print((-0).fraction)     // expect: -0
+System.print(0.123.fraction)    // expect: 0.123
+System.print(12.3.fraction)     // expect: 0.3
+System.print((-0.123).fraction) // expect: -0.123
+System.print((-12.3).fraction)  // expect: -0.3
 
 // Using 32-bit representation, a longer mantissa will lead to
 // approximation.
-IO.print((1.23456789012345).fraction)  // expect: 0.23456789012345
-IO.print((-1.23456789012345).fraction)  // expect: -0.23456789012345
+System.print((1.23456789012345).fraction)  // expect: 0.23456789012345
+System.print((-1.23456789012345).fraction)  // expect: -0.23456789012345
 
-IO.print((0.000000000000000000000000000000000000000001).fraction)  // expect: 1e-42
-IO.print((-0.000000000000000000000000000000000000000001).fraction)  // expect: -1e-42
+System.print((0.000000000000000000000000000000000000000001).fraction)  // expect: 1e-42
+System.print((-0.000000000000000000000000000000000000000001).fraction)  // expect: -1e-42
 
-IO.print((1.000000000000000000000000000000000000000001).fraction)  // expect: 0
-IO.print((-1.000000000000000000000000000000000000000001).fraction)  // expect: -0
+System.print((1.000000000000000000000000000000000000000001).fraction)  // expect: 0
+System.print((-1.000000000000000000000000000000000000000001).fraction)  // expect: -0
diff --git a/test/core/number/from_string.wren b/test/core/number/from_string.wren
index ef0ded91..30b47bbf 100644
--- a/test/core/number/from_string.wren
+++ b/test/core/number/from_string.wren
@@ -1,14 +1,14 @@
-IO.print(Num.fromString("123") == 123) // expect: true
-IO.print(Num.fromString("-123") == -123) // expect: true
-IO.print(Num.fromString("-0") == -0) // expect: true
-IO.print(Num.fromString("12.34") == 12.34) // expect: true
-IO.print(Num.fromString("-0.0001") == -0.0001) // expect: true
-IO.print(Num.fromString(" 12 ") == 12) // expect: true
+System.print(Num.fromString("123") == 123) // expect: true
+System.print(Num.fromString("-123") == -123) // expect: true
+System.print(Num.fromString("-0") == -0) // expect: true
+System.print(Num.fromString("12.34") == 12.34) // expect: true
+System.print(Num.fromString("-0.0001") == -0.0001) // expect: true
+System.print(Num.fromString(" 12 ") == 12) // expect: true
 
 // Test some non-number literals and ensure they return null.
-IO.print(Num.fromString("test1") == null) // expect: true
-IO.print(Num.fromString("") == null) // expect: true
-IO.print(Num.fromString("prefix1.2") == null) // expect: true
-IO.print(Num.fromString("1.2suffix") == null) // expect: true
+System.print(Num.fromString("test1") == null) // expect: true
+System.print(Num.fromString("") == null) // expect: true
+System.print(Num.fromString("prefix1.2") == null) // expect: true
+System.print(Num.fromString("1.2suffix") == null) // expect: true
 
 // TODO: Parse hex and scientific numbers.
diff --git a/test/core/number/is_nan.wren b/test/core/number/is_nan.wren
index 8d036501..5013c452 100644
--- a/test/core/number/is_nan.wren
+++ b/test/core/number/is_nan.wren
@@ -1,5 +1,5 @@
-IO.print(1.isNan)      // expect: false
-IO.print((0/0).isNan)  // expect: true
+System.print(1.isNan)      // expect: false
+System.print((0/0).isNan)  // expect: true
 
 // Infinity is not NaN.
-IO.print((1/0).isNan)  // expect: false
+System.print((1/0).isNan)  // expect: false
diff --git a/test/core/number/minus.wren b/test/core/number/minus.wren
index 3f5830be..bd59344f 100644
--- a/test/core/number/minus.wren
+++ b/test/core/number/minus.wren
@@ -1,8 +1,8 @@
 // Infix.
-IO.print(5 - 3)      // expect: 2
-IO.print(3.1 - 0.24) // expect: 2.86
-IO.print(3 - 2 - 1)  // expect: 0
+System.print(5 - 3)      // expect: 2
+System.print(3.1 - 0.24) // expect: 2.86
+System.print(3 - 2 - 1)  // expect: 0
 
 // Unary negation.
 var a = 3
-IO.print(-a) // expect: -3
+System.print(-a) // expect: -3
diff --git a/test/core/number/mod.wren b/test/core/number/mod.wren
index 30716a8c..67e35ade 100644
--- a/test/core/number/mod.wren
+++ b/test/core/number/mod.wren
@@ -1,17 +1,17 @@
-IO.print(5 % 3) // expect: 2
-IO.print(10 % 5) // expect: 0
-IO.print(-4 % 3) // expect: -1
-IO.print(4 % -3) // expect: 1
-IO.print(-4 % -3) // expect: -1
-IO.print(-4.2 % 3.1) // expect: -1.1
-IO.print(4.2 % -3.1) // expect: 1.1
-IO.print(-4.2 % -3.1) // expect: -1.1
+System.print(5 % 3) // expect: 2
+System.print(10 % 5) // expect: 0
+System.print(-4 % 3) // expect: -1
+System.print(4 % -3) // expect: 1
+System.print(-4 % -3) // expect: -1
+System.print(-4.2 % 3.1) // expect: -1.1
+System.print(4.2 % -3.1) // expect: 1.1
+System.print(-4.2 % -3.1) // expect: -1.1
 
 // Left associative.
-IO.print(13 % 7 % 4) // expect: 2
+System.print(13 % 7 % 4) // expect: 2
 
 // Precedence.
-IO.print(13 + 1 % 7) // expect: 14
+System.print(13 + 1 % 7) // expect: 14
 
 // TODO: Unsupported RHS types.
 // TODO: Error on mod by zero.
diff --git a/test/core/number/multiply.wren b/test/core/number/multiply.wren
index bb615150..7705d63a 100644
--- a/test/core/number/multiply.wren
+++ b/test/core/number/multiply.wren
@@ -1,2 +1,2 @@
-IO.print(5 * 3) // expect: 15
-IO.print(12.34 * 0.3) // expect: 3.702
+System.print(5 * 3) // expect: 15
+System.print(12.34 * 0.3) // expect: 3.702
diff --git a/test/core/number/not.wren b/test/core/number/not.wren
index 87fcd1da..0b296248 100644
--- a/test/core/number/not.wren
+++ b/test/core/number/not.wren
@@ -1,2 +1,2 @@
-IO.print(!123) // expect: false
-IO.print(!0) // expect: false
+System.print(!123) // expect: false
+System.print(!0) // expect: false
diff --git a/test/core/number/plus.wren b/test/core/number/plus.wren
index 5b5290b7..14385494 100644
--- a/test/core/number/plus.wren
+++ b/test/core/number/plus.wren
@@ -1,3 +1,3 @@
-IO.print(1 + 2) // expect: 3
-IO.print(12.34 + 0.13) // expect: 12.47
-IO.print(3 + 5 + 2) // expect: 10
+System.print(1 + 2) // expect: 3
+System.print(12.34 + 0.13) // expect: 12.47
+System.print(3 + 5 + 2) // expect: 10
diff --git a/test/core/number/sign.wren b/test/core/number/sign.wren
index b6546901..e728cb10 100644
--- a/test/core/number/sign.wren
+++ b/test/core/number/sign.wren
@@ -1,6 +1,6 @@
-IO.print(123.sign)      // expect: 1
-IO.print((-123).sign)   // expect: -1
-IO.print(0.sign)        // expect: 0
-IO.print((-0).sign)     // expect: 0
-IO.print(0.123.sign)    // expect: 1
-IO.print((-0.123).sign) // expect: -1
+System.print(123.sign)      // expect: 1
+System.print((-123).sign)   // expect: -1
+System.print(0.sign)        // expect: 0
+System.print((-0).sign)     // expect: 0
+System.print(0.123.sign)    // expect: 1
+System.print((-0.123).sign) // expect: -1
diff --git a/test/core/number/sin.wren b/test/core/number/sin.wren
index da2218e9..e83c1073 100644
--- a/test/core/number/sin.wren
+++ b/test/core/number/sin.wren
@@ -1,6 +1,6 @@
-IO.print(0.sin)             // expect: 0
-IO.print((Num.pi / 2).sin)  // expect: 1
+System.print(0.sin)             // expect: 0
+System.print((Num.pi / 2).sin)  // expect: 1
 
 // these should of course be 0, but it's not that precise
-IO.print(Num.pi.sin)        // expect: 1.2246467991474e-16
-IO.print((2 * Num.pi).sin)  // expect: -2.4492935982947e-16
+System.print(Num.pi.sin)        // expect: 1.2246467991474e-16
+System.print((2 * Num.pi).sin)  // expect: -2.4492935982947e-16
diff --git a/test/core/number/sqrt.wren b/test/core/number/sqrt.wren
index f14cf979..fb5591f9 100644
--- a/test/core/number/sqrt.wren
+++ b/test/core/number/sqrt.wren
@@ -1,10 +1,10 @@
-IO.print(4.sqrt)        // expect: 2
-IO.print(1000000.sqrt)  // expect: 1000
-IO.print(1.sqrt)        // expect: 1
-IO.print((-0).sqrt)     // expect: -0
-IO.print(0.sqrt)        // expect: 0
-IO.print(2.sqrt)        // expect: 1.4142135623731
+System.print(4.sqrt)        // expect: 2
+System.print(1000000.sqrt)  // expect: 1000
+System.print(1.sqrt)        // expect: 1
+System.print((-0).sqrt)     // expect: -0
+System.print(0.sqrt)        // expect: 0
+System.print(2.sqrt)        // expect: 1.4142135623731
 
-IO.print((-4).sqrt.isNan) // expect: true
+System.print((-4).sqrt.isNan) // expect: true
 
 // TODO: Tests for sin and cos.
diff --git a/test/core/number/tan.wren b/test/core/number/tan.wren
index 7173db4b..6e89ae2b 100644
--- a/test/core/number/tan.wren
+++ b/test/core/number/tan.wren
@@ -1,3 +1,3 @@
-IO.print(0.tan)             // expect: 0
-IO.print((Num.pi / 4).tan)  // expect: 1
-IO.print((-Num.pi / 4).tan) // expect: -1
+System.print(0.tan)             // expect: 0
+System.print((Num.pi / 4).tan)  // expect: 1
+System.print((-Num.pi / 4).tan) // expect: -1
diff --git a/test/core/number/to_string.wren b/test/core/number/to_string.wren
index 4ba6f896..60c32c9c 100644
--- a/test/core/number/to_string.wren
+++ b/test/core/number/to_string.wren
@@ -1,5 +1,5 @@
-IO.print(123.toString == "123") // expect: true
-IO.print((-123).toString == "-123") // expect: true
-IO.print((-0).toString == "-0") // expect: true
-IO.print(12.34.toString == "12.34") // expect: true
-IO.print((-0.0001).toString == "-0.0001") // expect: true
+System.print(123.toString == "123") // expect: true
+System.print((-123).toString == "-123") // expect: true
+System.print((-0).toString == "-0") // expect: true
+System.print(12.34.toString == "12.34") // expect: true
+System.print((-0.0001).toString == "-0.0001") // expect: true
diff --git a/test/core/number/truncate.wren b/test/core/number/truncate.wren
index dfc68c40..023d3d59 100644
--- a/test/core/number/truncate.wren
+++ b/test/core/number/truncate.wren
@@ -1,13 +1,13 @@
-IO.print(123.truncate)      // expect: 123
-IO.print((-123).truncate)   // expect: -123
-IO.print(0.truncate)        // expect: 0
-IO.print((-0).truncate)     // expect: -0
-IO.print(0.123.truncate)    // expect: 0
-IO.print(12.3.truncate)     // expect: 12
-IO.print((-0.123).truncate) // expect: -0
-IO.print((-12.3).truncate)  // expect: -12
+System.print(123.truncate)      // expect: 123
+System.print((-123).truncate)   // expect: -123
+System.print(0.truncate)        // expect: 0
+System.print((-0).truncate)     // expect: -0
+System.print(0.123.truncate)    // expect: 0
+System.print(12.3.truncate)     // expect: 12
+System.print((-0.123).truncate) // expect: -0
+System.print((-12.3).truncate)  // expect: -12
 
 // Using 32-bit representation, values "beyond" those  two will lead to
 // approximation.
-IO.print((12345678901234.5).truncate)   // expect: 12345678901234
-IO.print((-12345678901234.5).truncate)  // expect: -12345678901234
+System.print((12345678901234.5).truncate)   // expect: 12345678901234
+System.print((-12345678901234.5).truncate)  // expect: -12345678901234
diff --git a/test/core/number/type.wren b/test/core/number/type.wren
index bf7a65a8..9ff74651 100644
--- a/test/core/number/type.wren
+++ b/test/core/number/type.wren
@@ -1,4 +1,4 @@
-IO.print(123 is Num)      // expect: true
-IO.print(123 is Object)   // expect: true
-IO.print(123 is String)   // expect: false
-IO.print(123.type == Num) // expect: true
+System.print(123 is Num)      // expect: true
+System.print(123 is Object)   // expect: true
+System.print(123 is String)   // expect: false
+System.print(123.type == Num) // expect: true
diff --git a/test/core/object/not.wren b/test/core/object/not.wren
index d658d6fb..ab97e577 100644
--- a/test/core/object/not.wren
+++ b/test/core/object/not.wren
@@ -1,4 +1,4 @@
 class Foo {
   construct new() {}
 }
-IO.print(!Foo.new()) // expect: false
+System.print(!Foo.new()) // expect: false
diff --git a/test/core/object/same.wren b/test/core/object/same.wren
index 43b51494..9111aee8 100644
--- a/test/core/object/same.wren
+++ b/test/core/object/same.wren
@@ -1,27 +1,27 @@
 // Value types compare by value.
-IO.print(Object.same(true, true)) // expect: true
-IO.print(Object.same(true, false)) // expect: false
+System.print(Object.same(true, true)) // expect: true
+System.print(Object.same(true, false)) // expect: false
 
-IO.print(Object.same(null, null)) // expect: true
+System.print(Object.same(null, null)) // expect: true
 
-IO.print(Object.same(1 + 2, 2 + 1)) // expect: true
-IO.print(Object.same(1 + 2, 2 + 2)) // expect: false
+System.print(Object.same(1 + 2, 2 + 1)) // expect: true
+System.print(Object.same(1 + 2, 2 + 2)) // expect: false
 
-IO.print(Object.same(1..2, 1..2)) // expect: true
-IO.print(Object.same(1..2, 1..3)) // expect: false
+System.print(Object.same(1..2, 1..2)) // expect: true
+System.print(Object.same(1..2, 1..3)) // expect: false
 
-IO.print(Object.same("ab", "a" + "b")) // expect: true
-IO.print(Object.same("ab", "a" + "c")) // expect: false
+System.print(Object.same("ab", "a" + "b")) // expect: true
+System.print(Object.same("ab", "a" + "c")) // expect: false
 
 // Different types are never the same.
-IO.print(Object.same(null, false)) // expect: false
-IO.print(Object.same(true, 2)) // expect: false
-IO.print(Object.same(1..2, 2)) // expect: false
-IO.print(Object.same("1", 1)) // expect: false
+System.print(Object.same(null, false)) // expect: false
+System.print(Object.same(true, 2)) // expect: false
+System.print(Object.same(1..2, 2)) // expect: false
+System.print(Object.same("1", 1)) // expect: false
 
 // Classes compare by identity.
-IO.print(Object.same(Bool, Num)) // expect: false
-IO.print(Object.same(Bool, Bool)) // expect: true
+System.print(Object.same(Bool, Num)) // expect: false
+System.print(Object.same(Bool, Bool)) // expect: true
 
 // Other types compare by identity.
 class Foo {
@@ -29,8 +29,8 @@ class Foo {
 }
 
 var foo = Foo.new()
-IO.print(Object.same(foo, foo)) // expect: true
-IO.print(Object.same(foo, Foo.new())) // expect: false
+System.print(Object.same(foo, foo)) // expect: true
+System.print(Object.same(foo, Foo.new())) // expect: false
 
 // Ignores == operators.
 class Bar {
@@ -39,5 +39,5 @@ class Bar {
 }
 
 var bar = Bar.new()
-IO.print(Object.same(bar, bar)) // expect: true
-IO.print(Object.same(bar, Bar.new())) // expect: false
+System.print(Object.same(bar, bar)) // expect: true
+System.print(Object.same(bar, Bar.new())) // expect: false
diff --git a/test/core/object/to_string.wren b/test/core/object/to_string.wren
index 59d44126..3037066e 100644
--- a/test/core/object/to_string.wren
+++ b/test/core/object/to_string.wren
@@ -1,4 +1,4 @@
 class Foo {
   construct new() {}
 }
-IO.print(Foo.new().toString == "instance of Foo") // expect: true
+System.print(Foo.new().toString == "instance of Foo") // expect: true
diff --git a/test/core/object/type.wren b/test/core/object/type.wren
index db1c51cd..0e46c805 100644
--- a/test/core/object/type.wren
+++ b/test/core/object/type.wren
@@ -1,13 +1,13 @@
 class Foo {}
 
 // Object's class is a class.
-IO.print(Object is Class) // expect: true
+System.print(Object is Class) // expect: true
 
 // Its metatype is also a class.
-IO.print(Object.type is Class) // expect: true
+System.print(Object.type is Class) // expect: true
 
 // The metatype's metatype is Class.
-IO.print(Object.type.type == Class) // expect: true
+System.print(Object.type.type == Class) // expect: true
 
 // Object has a distinct metaclass.
-IO.print(Object.type.name) // expect: Object metaclass
+System.print(Object.type.name) // expect: Object metaclass
diff --git a/test/core/range/contains.wren b/test/core/range/contains.wren
index 97189ef6..d6be1ea1 100644
--- a/test/core/range/contains.wren
+++ b/test/core/range/contains.wren
@@ -1,23 +1,23 @@
 // Ordered range.
-IO.print((2..5).contains(1)) // expect: false
-IO.print((2..5).contains(2)) // expect: true
-IO.print((2..5).contains(5)) // expect: true
-IO.print((2..5).contains(6)) // expect: false
+System.print((2..5).contains(1)) // expect: false
+System.print((2..5).contains(2)) // expect: true
+System.print((2..5).contains(5)) // expect: true
+System.print((2..5).contains(6)) // expect: false
 
 // Backwards range.
-IO.print((5..2).contains(1)) // expect: false
-IO.print((5..2).contains(2)) // expect: true
-IO.print((5..2).contains(5)) // expect: true
-IO.print((5..2).contains(6)) // expect: false
+System.print((5..2).contains(1)) // expect: false
+System.print((5..2).contains(2)) // expect: true
+System.print((5..2).contains(5)) // expect: true
+System.print((5..2).contains(6)) // expect: false
 
 // Exclusive ordered range.
-IO.print((2...5).contains(1)) // expect: false
-IO.print((2...5).contains(2)) // expect: true
-IO.print((2...5).contains(5)) // expect: false
-IO.print((2...5).contains(6)) // expect: false
+System.print((2...5).contains(1)) // expect: false
+System.print((2...5).contains(2)) // expect: true
+System.print((2...5).contains(5)) // expect: false
+System.print((2...5).contains(6)) // expect: false
 
 // Exclusive backwards range.
-IO.print((5...2).contains(1)) // expect: false
-IO.print((5...2).contains(2)) // expect: false
-IO.print((5...2).contains(5)) // expect: true
-IO.print((5...2).contains(6)) // expect: false
+System.print((5...2).contains(1)) // expect: false
+System.print((5...2).contains(2)) // expect: false
+System.print((5...2).contains(5)) // expect: true
+System.print((5...2).contains(6)) // expect: false
diff --git a/test/core/range/equality.wren b/test/core/range/equality.wren
index a2e23d30..9cf77676 100644
--- a/test/core/range/equality.wren
+++ b/test/core/range/equality.wren
@@ -3,15 +3,15 @@ var b = 2..6
 var c = 2...5
 var d = 2...6
 
-IO.print(a == 2..5) // expect: true
-IO.print(a == 2..6) // expect: false
-IO.print(c == 2...5) // expect: true
-IO.print(c == 2...6) // expect: false
+System.print(a == 2..5) // expect: true
+System.print(a == 2..6) // expect: false
+System.print(c == 2...5) // expect: true
+System.print(c == 2...6) // expect: false
 
-IO.print(b != 2..5) // expect: true
-IO.print(b != 2..6) // expect: false
-IO.print(d != 2...5) // expect: true
-IO.print(d != 2...6) // expect: false
+System.print(b != 2..5) // expect: true
+System.print(b != 2..6) // expect: false
+System.print(d != 2...5) // expect: true
+System.print(d != 2...6) // expect: false
 
-IO.print(a != c) // expect: true
-IO.print(b != d) // expect: true
\ No newline at end of file
+System.print(a != c) // expect: true
+System.print(b != d) // expect: true
\ No newline at end of file
diff --git a/test/core/range/floating_point.wren b/test/core/range/floating_point.wren
index 114ea1fb..78f7ff13 100644
--- a/test/core/range/floating_point.wren
+++ b/test/core/range/floating_point.wren
@@ -1,25 +1,25 @@
 // Ordered range.
-IO.print((2..5).from) // expect: 2
-IO.print((3..3).from) // expect: 3
-IO.print((0..3).from) // expect: 0
-IO.print((-5..3).from) // expect: -5
-IO.print((-5..-2).from) // expect: -5
+System.print((2..5).from) // expect: 2
+System.print((3..3).from) // expect: 3
+System.print((0..3).from) // expect: 0
+System.print((-5..3).from) // expect: -5
+System.print((-5..-2).from) // expect: -5
 
 // Backwards range.
-IO.print((5..2).from) // expect: 5
-IO.print((3..0).from) // expect: 3
-IO.print((3..-5).from) // expect: 3
-IO.print((-2..-5).from) // expect: -2
+System.print((5..2).from) // expect: 5
+System.print((3..0).from) // expect: 3
+System.print((3..-5).from) // expect: 3
+System.print((-2..-5).from) // expect: -2
 
 // Exclusive ordered range.
-IO.print((2...5).from) // expect: 2
-IO.print((3...3).from) // expect: 3
-IO.print((0...3).from) // expect: 0
-IO.print((-5...3).from) // expect: -5
-IO.print((-5...-2).from) // expect: -5
+System.print((2...5).from) // expect: 2
+System.print((3...3).from) // expect: 3
+System.print((0...3).from) // expect: 0
+System.print((-5...3).from) // expect: -5
+System.print((-5...-2).from) // expect: -5
 
 // Exclusive backwards range.
-IO.print((5...2).from) // expect: 5
-IO.print((3...0).from) // expect: 3
-IO.print((3...-5).from) // expect: 3
-IO.print((-2...-5).from) // expect: -2
+System.print((5...2).from) // expect: 5
+System.print((3...0).from) // expect: 3
+System.print((3...-5).from) // expect: 3
+System.print((-2...-5).from) // expect: -2
diff --git a/test/core/range/from.wren b/test/core/range/from.wren
index 114ea1fb..78f7ff13 100644
--- a/test/core/range/from.wren
+++ b/test/core/range/from.wren
@@ -1,25 +1,25 @@
 // Ordered range.
-IO.print((2..5).from) // expect: 2
-IO.print((3..3).from) // expect: 3
-IO.print((0..3).from) // expect: 0
-IO.print((-5..3).from) // expect: -5
-IO.print((-5..-2).from) // expect: -5
+System.print((2..5).from) // expect: 2
+System.print((3..3).from) // expect: 3
+System.print((0..3).from) // expect: 0
+System.print((-5..3).from) // expect: -5
+System.print((-5..-2).from) // expect: -5
 
 // Backwards range.
-IO.print((5..2).from) // expect: 5
-IO.print((3..0).from) // expect: 3
-IO.print((3..-5).from) // expect: 3
-IO.print((-2..-5).from) // expect: -2
+System.print((5..2).from) // expect: 5
+System.print((3..0).from) // expect: 3
+System.print((3..-5).from) // expect: 3
+System.print((-2..-5).from) // expect: -2
 
 // Exclusive ordered range.
-IO.print((2...5).from) // expect: 2
-IO.print((3...3).from) // expect: 3
-IO.print((0...3).from) // expect: 0
-IO.print((-5...3).from) // expect: -5
-IO.print((-5...-2).from) // expect: -5
+System.print((2...5).from) // expect: 2
+System.print((3...3).from) // expect: 3
+System.print((0...3).from) // expect: 0
+System.print((-5...3).from) // expect: -5
+System.print((-5...-2).from) // expect: -5
 
 // Exclusive backwards range.
-IO.print((5...2).from) // expect: 5
-IO.print((3...0).from) // expect: 3
-IO.print((3...-5).from) // expect: 3
-IO.print((-2...-5).from) // expect: -2
+System.print((5...2).from) // expect: 5
+System.print((3...0).from) // expect: 3
+System.print((3...-5).from) // expect: 3
+System.print((-2...-5).from) // expect: -2
diff --git a/test/core/range/is_inclusive.wren b/test/core/range/is_inclusive.wren
index 8f881aef..bd7e89fa 100644
--- a/test/core/range/is_inclusive.wren
+++ b/test/core/range/is_inclusive.wren
@@ -1,5 +1,5 @@
-IO.print((0..0).isInclusive) // expect: true
-IO.print((0...0).isInclusive) // expect: false
+System.print((0..0).isInclusive) // expect: true
+System.print((0...0).isInclusive) // expect: false
 
-IO.print((-1..1).isInclusive) // expect: true
-IO.print((-1...1).isInclusive) // expect: false
+System.print((-1..1).isInclusive) // expect: true
+System.print((-1...1).isInclusive) // expect: false
diff --git a/test/core/range/iterate.wren b/test/core/range/iterate.wren
index db4e949d..3de968e9 100644
--- a/test/core/range/iterate.wren
+++ b/test/core/range/iterate.wren
@@ -1,35 +1,35 @@
 // Inclusive.
 var range = 1..3
-IO.print(range.iterate(null)) // expect: 1
-IO.print(range.iterate(1)) // expect: 2
-IO.print(range.iterate(2)) // expect: 3
-IO.print(range.iterate(3)) // expect: false
-IO.print(range.iterate(4)) // expect: false
+System.print(range.iterate(null)) // expect: 1
+System.print(range.iterate(1)) // expect: 2
+System.print(range.iterate(2)) // expect: 3
+System.print(range.iterate(3)) // expect: false
+System.print(range.iterate(4)) // expect: false
 
 // Exclusive
 range = 1...3
-IO.print(range.iterate(null)) // expect: 1
-IO.print(range.iterate(1)) // expect: 2
-IO.print(range.iterate(2)) // expect: false
+System.print(range.iterate(null)) // expect: 1
+System.print(range.iterate(1)) // expect: 2
+System.print(range.iterate(2)) // expect: false
 
 // Negative inclusive range.
 range = 3..1
-IO.print(range.iterate(null)) // expect: 3
-IO.print(range.iterate(3)) // expect: 2
-IO.print(range.iterate(2)) // expect: 1
-IO.print(range.iterate(1)) // expect: false
+System.print(range.iterate(null)) // expect: 3
+System.print(range.iterate(3)) // expect: 2
+System.print(range.iterate(2)) // expect: 1
+System.print(range.iterate(1)) // expect: false
 
 // Negative exclusive range.
 range = 3...1
-IO.print(range.iterate(null)) // expect: 3
-IO.print(range.iterate(3)) // expect: 2
-IO.print(range.iterate(2)) // expect: false
+System.print(range.iterate(null)) // expect: 3
+System.print(range.iterate(3)) // expect: 2
+System.print(range.iterate(2)) // expect: false
 
 // Empty inclusive range.
 range = 1..1
-IO.print(range.iterate(null)) // expect: 1
-IO.print(range.iterate(1)) // expect: false
+System.print(range.iterate(null)) // expect: 1
+System.print(range.iterate(1)) // expect: false
 
 // Empty exclusive range.
 range = 1...1
-IO.print(range.iterate(null)) // expect: false
+System.print(range.iterate(null)) // expect: false
diff --git a/test/core/range/iterate_from_float.wren b/test/core/range/iterate_from_float.wren
index 23e7ca41..1e02c7de 100644
--- a/test/core/range/iterate_from_float.wren
+++ b/test/core/range/iterate_from_float.wren
@@ -1,18 +1,18 @@
 // Starts at "from" and adds 1.0 each iteration.
 
-for (n in 1.3..4.5) IO.print(n)
+for (n in 1.3..4.5) System.print(n)
 // expect: 1.3
 // expect: 2.3
 // expect: 3.3
 // expect: 4.3
 
-for (n in 1.3...4.5) IO.print(n)
+for (n in 1.3...4.5) System.print(n)
 // expect: 1.3
 // expect: 2.3
 // expect: 3.3
 // expect: 4.3
 
-for (n in 1.3...4.3) IO.print(n)
+for (n in 1.3...4.3) System.print(n)
 // expect: 1.3
 // expect: 2.3
 // expect: 3.3
diff --git a/test/core/range/iterator_value.wren b/test/core/range/iterator_value.wren
index 5274517e..28139701 100644
--- a/test/core/range/iterator_value.wren
+++ b/test/core/range/iterator_value.wren
@@ -1,11 +1,11 @@
 var range = 1..3
-IO.print(range.iteratorValue(1)) // expect: 1
-IO.print(range.iteratorValue(2)) // expect: 2
-IO.print(range.iteratorValue(3)) // expect: 3
+System.print(range.iteratorValue(1)) // expect: 1
+System.print(range.iteratorValue(2)) // expect: 2
+System.print(range.iteratorValue(3)) // expect: 3
 
 // Doesn't bother to bounds check.
-IO.print(range.iteratorValue(-2)) // expect: -2
-IO.print(range.iteratorValue(5)) // expect: 5
+System.print(range.iteratorValue(-2)) // expect: -2
+System.print(range.iteratorValue(5)) // expect: 5
 
 // Or type check.
-IO.print(range.iteratorValue("s")) // expect: s
+System.print(range.iteratorValue("s")) // expect: s
diff --git a/test/core/range/join.wren b/test/core/range/join.wren
index 81c336a1..46a58beb 100644
--- a/test/core/range/join.wren
+++ b/test/core/range/join.wren
@@ -1,4 +1,4 @@
 var a = 1..3
 
-IO.print(a.join) // expect: 123
-IO.print(a.join(", ")) // expect: 1, 2, 3
+System.print(a.join) // expect: 123
+System.print(a.join(", ")) // expect: 1, 2, 3
diff --git a/test/core/range/map.wren b/test/core/range/map.wren
index 2d65317e..1081c8b1 100644
--- a/test/core/range/map.wren
+++ b/test/core/range/map.wren
@@ -1,3 +1,3 @@
 var a = 1..3
 var b = a.map {|x| x + 1 }.toList
-IO.print(b) // expect: [2, 3, 4]
+System.print(b) // expect: [2, 3, 4]
diff --git a/test/core/range/max.wren b/test/core/range/max.wren
index 9c6672d2..70aa0b67 100644
--- a/test/core/range/max.wren
+++ b/test/core/range/max.wren
@@ -1,25 +1,25 @@
 // Ordered range.
-IO.print((2..5).max) // expect: 5
-IO.print((3..3).max) // expect: 3
-IO.print((0..3).max) // expect: 3
-IO.print((-5..3).max) // expect: 3
-IO.print((-5..-2).max) // expect: -2
+System.print((2..5).max) // expect: 5
+System.print((3..3).max) // expect: 3
+System.print((0..3).max) // expect: 3
+System.print((-5..3).max) // expect: 3
+System.print((-5..-2).max) // expect: -2
 
 // Backwards range.
-IO.print((5..2).max) // expect: 5
-IO.print((3..0).max) // expect: 3
-IO.print((3..-5).max) // expect: 3
-IO.print((-2..-5).max) // expect: -2
+System.print((5..2).max) // expect: 5
+System.print((3..0).max) // expect: 3
+System.print((3..-5).max) // expect: 3
+System.print((-2..-5).max) // expect: -2
 
 // Exclusive ordered range.
-IO.print((2...5).max) // expect: 5
-IO.print((3...3).max) // expect: 3
-IO.print((0...3).max) // expect: 3
-IO.print((-5...3).max) // expect: 3
-IO.print((-5...-2).max) // expect: -2
+System.print((2...5).max) // expect: 5
+System.print((3...3).max) // expect: 3
+System.print((0...3).max) // expect: 3
+System.print((-5...3).max) // expect: 3
+System.print((-5...-2).max) // expect: -2
 
 // Exclusive backwards range.
-IO.print((5...2).max) // expect: 5
-IO.print((3...0).max) // expect: 3
-IO.print((3...-5).max) // expect: 3
-IO.print((-2...-5).max) // expect: -2
+System.print((5...2).max) // expect: 5
+System.print((3...0).max) // expect: 3
+System.print((3...-5).max) // expect: 3
+System.print((-2...-5).max) // expect: -2
diff --git a/test/core/range/min.wren b/test/core/range/min.wren
index bcc019bf..a6dcaa96 100644
--- a/test/core/range/min.wren
+++ b/test/core/range/min.wren
@@ -1,25 +1,25 @@
 // Ordered range.
-IO.print((2..5).min) // expect: 2
-IO.print((3..3).min) // expect: 3
-IO.print((0..3).min) // expect: 0
-IO.print((-5..3).min) // expect: -5
-IO.print((-5..-2).min) // expect: -5
+System.print((2..5).min) // expect: 2
+System.print((3..3).min) // expect: 3
+System.print((0..3).min) // expect: 0
+System.print((-5..3).min) // expect: -5
+System.print((-5..-2).min) // expect: -5
 
 // Backwards range.
-IO.print((5..2).min) // expect: 2
-IO.print((3..0).min) // expect: 0
-IO.print((3..-5).min) // expect: -5
-IO.print((-2..-5).min) // expect: -5
+System.print((5..2).min) // expect: 2
+System.print((3..0).min) // expect: 0
+System.print((3..-5).min) // expect: -5
+System.print((-2..-5).min) // expect: -5
 
 // Exclusive ordered range.
-IO.print((2...5).min) // expect: 2
-IO.print((3...3).min) // expect: 3
-IO.print((0...3).min) // expect: 0
-IO.print((-5...3).min) // expect: -5
-IO.print((-5...-2).min) // expect: -5
+System.print((2...5).min) // expect: 2
+System.print((3...3).min) // expect: 3
+System.print((0...3).min) // expect: 0
+System.print((-5...3).min) // expect: -5
+System.print((-5...-2).min) // expect: -5
 
 // Exclusive backwards range.
-IO.print((5...2).min) // expect: 2
-IO.print((3...0).min) // expect: 0
-IO.print((3...-5).min) // expect: -5
-IO.print((-2...-5).min) // expect: -5
+System.print((5...2).min) // expect: 2
+System.print((3...0).min) // expect: 0
+System.print((3...-5).min) // expect: -5
+System.print((-2...-5).min) // expect: -5
diff --git a/test/core/range/reduce.wren b/test/core/range/reduce.wren
index 2df9c295..30e88b39 100644
--- a/test/core/range/reduce.wren
+++ b/test/core/range/reduce.wren
@@ -1,4 +1,4 @@
 var range = 1..10
 
-IO.print(range.reduce {|a, b| a + b }) // expect: 55
-IO.print(range.reduce(100) {|a, b| a < b ? a : b }) // expect: 1
+System.print(range.reduce {|a, b| a + b }) // expect: 55
+System.print(range.reduce(100) {|a, b| a < b ? a : b }) // expect: 1
diff --git a/test/core/range/to.wren b/test/core/range/to.wren
index ad3a5444..8a9d864b 100644
--- a/test/core/range/to.wren
+++ b/test/core/range/to.wren
@@ -1,25 +1,25 @@
 // Ordered range.
-IO.print((2..5).to) // expect: 5
-IO.print((3..3).to) // expect: 3
-IO.print((0..3).to) // expect: 3
-IO.print((-5..3).to) // expect: 3
-IO.print((-5..-2).to) // expect: -2
+System.print((2..5).to) // expect: 5
+System.print((3..3).to) // expect: 3
+System.print((0..3).to) // expect: 3
+System.print((-5..3).to) // expect: 3
+System.print((-5..-2).to) // expect: -2
 
 // Backwards range.
-IO.print((5..2).to) // expect: 2
-IO.print((3..0).to) // expect: 0
-IO.print((3..-5).to) // expect: -5
-IO.print((-2..-5).to) // expect: -5
+System.print((5..2).to) // expect: 2
+System.print((3..0).to) // expect: 0
+System.print((3..-5).to) // expect: -5
+System.print((-2..-5).to) // expect: -5
 
 // Exclusive ordered range.
-IO.print((2...5).to) // expect: 5
-IO.print((3...3).to) // expect: 3
-IO.print((0...3).to) // expect: 3
-IO.print((-5...3).to) // expect: 3
-IO.print((-5...-2).to) // expect: -2
+System.print((2...5).to) // expect: 5
+System.print((3...3).to) // expect: 3
+System.print((0...3).to) // expect: 3
+System.print((-5...3).to) // expect: 3
+System.print((-5...-2).to) // expect: -2
 
 // Exclusive backwards range.
-IO.print((5...2).to) // expect: 2
-IO.print((3...0).to) // expect: 0
-IO.print((3...-5).to) // expect: -5
-IO.print((-2...-5).to) // expect: -5
+System.print((5...2).to) // expect: 2
+System.print((3...0).to) // expect: 0
+System.print((3...-5).to) // expect: -5
+System.print((-2...-5).to) // expect: -5
diff --git a/test/core/range/to_string.wren b/test/core/range/to_string.wren
index 795b0d3e..d3e6c698 100644
--- a/test/core/range/to_string.wren
+++ b/test/core/range/to_string.wren
@@ -1,7 +1,7 @@
-IO.print(1..3) // expect: 1..3
-IO.print(12345.6789..12345.6789) // expect: 12345.6789..12345.6789
-IO.print(-100..-300) // expect: -100..-300
+System.print(1..3) // expect: 1..3
+System.print(12345.6789..12345.6789) // expect: 12345.6789..12345.6789
+System.print(-100..-300) // expect: -100..-300
 
-IO.print(1...3) // expect: 1...3
-IO.print(12345.6789...12345.6789) // expect: 12345.6789...12345.6789
-IO.print(-100...-300) // expect: -100...-300
+System.print(1...3) // expect: 1...3
+System.print(12345.6789...12345.6789) // expect: 12345.6789...12345.6789
+System.print(-100...-300) // expect: -100...-300
diff --git a/test/core/range/type.wren b/test/core/range/type.wren
index 56f5b85e..2f748b3a 100644
--- a/test/core/range/type.wren
+++ b/test/core/range/type.wren
@@ -1,7 +1,7 @@
 var range = 2..5
 
-IO.print(range is Range)      // expect: true
-IO.print(range is Sequence)   // expect: true
-IO.print(range is Object)     // expect: true
-IO.print(range is String)     // expect: false
-IO.print(range.type == Range) // expect: true
+System.print(range is Range)      // expect: true
+System.print(range is Sequence)   // expect: true
+System.print(range is Object)     // expect: true
+System.print(range is String)     // expect: false
+System.print(range.type == Range) // expect: true
diff --git a/test/core/range/where.wren b/test/core/range/where.wren
index 33aa9991..ce52210e 100644
--- a/test/core/range/where.wren
+++ b/test/core/range/where.wren
@@ -1,6 +1,6 @@
 var a = 1..3
 var b = a.where {|x| x > 1 }.toList
-IO.print(b) // expect: [2, 3]
+System.print(b) // expect: [2, 3]
 
 var c = a.where {|x| x > 10 }.toList
-IO.print(c) // expect: []
+System.print(c) // expect: []
diff --git a/test/core/sequence/all.wren b/test/core/sequence/all.wren
index 5b26f05a..265d20f8 100644
--- a/test/core/sequence/all.wren
+++ b/test/core/sequence/all.wren
@@ -1,10 +1,10 @@
 var a = [1, 2, 3]
-IO.print(a.all {|x| x > 1 }) // expect: false
-IO.print(a.all {|x| x > 0 }) // expect: true
-IO.print([].all {|x| false }) // expect: true
+System.print(a.all {|x| x > 1 }) // expect: false
+System.print(a.all {|x| x > 0 }) // expect: true
+System.print([].all {|x| false }) // expect: true
 
 // Returns first falsey value.
-IO.print(a.all {|x| x < 2 ? null : false }) // expect: null
+System.print(a.all {|x| x < 2 ? null : false }) // expect: null
 
 // Returns last truthy value.
-IO.print(a.all {|x| x }) // expect: 3
\ No newline at end of file
+System.print(a.all {|x| x }) // expect: 3
\ No newline at end of file
diff --git a/test/core/sequence/any.wren b/test/core/sequence/any.wren
index c60d70c8..7ffac07a 100644
--- a/test/core/sequence/any.wren
+++ b/test/core/sequence/any.wren
@@ -1,10 +1,10 @@
 var a = [1, 2, 3]
-IO.print(a.any {|x| x > 3 }) // expect: false
-IO.print(a.any {|x| x > 1 }) // expect: true
-IO.print([].any {|x| true }) // expect: false
+System.print(a.any {|x| x > 3 }) // expect: false
+System.print(a.any {|x| x > 1 }) // expect: true
+System.print([].any {|x| true }) // expect: false
 
 // Returns first truthy value.
-IO.print(a.any {|x| x }) // expect: 1
+System.print(a.any {|x| x }) // expect: 1
 
 // Returns last falsey value.
-IO.print(a.any {|x| x < 2 ? null : false }) // expect: false
+System.print(a.any {|x| x < 2 ? null : false }) // expect: false
diff --git a/test/core/sequence/count.wren b/test/core/sequence/count.wren
index 959026f8..05960819 100644
--- a/test/core/sequence/count.wren
+++ b/test/core/sequence/count.wren
@@ -10,4 +10,4 @@ class TestSequence is Sequence {
   iteratorValue(iterator) { iterator }
 }
 
-IO.print(TestSequence.new().count) // expect: 10
+System.print(TestSequence.new().count) // expect: 10
diff --git a/test/core/sequence/is_empty.wren b/test/core/sequence/is_empty.wren
index 5134d608..89513637 100644
--- a/test/core/sequence/is_empty.wren
+++ b/test/core/sequence/is_empty.wren
@@ -1,5 +1,5 @@
-IO.print([].isEmpty) // expect: true
-IO.print([1].isEmpty) // expect: false
+System.print([].isEmpty) // expect: true
+System.print([1].isEmpty) // expect: false
 
 class InfiniteSequence is Sequence {
   construct new() {}
@@ -8,4 +8,4 @@ class InfiniteSequence is Sequence {
 }
 
 // Should not try to iterate the whole sequence.
-IO.print(InfiniteSequence.new().isEmpty) // expect: false
+System.print(InfiniteSequence.new().isEmpty) // expect: false
diff --git a/test/core/sequence/map.wren b/test/core/sequence/map.wren
index cb9833a2..d963ff3d 100644
--- a/test/core/sequence/map.wren
+++ b/test/core/sequence/map.wren
@@ -29,20 +29,20 @@ class Fib is Sequence {
 var squareFib = Fib.new().map {|fib| fib * fib }
 var iterator = null
 
-IO.print(squareFib is Sequence) // expect: true
-IO.print(squareFib) // expect: instance of MapSequence
+System.print(squareFib is Sequence) // expect: true
+System.print(squareFib) // expect: instance of MapSequence
 
 iterator = squareFib.iterate(iterator)
-IO.print(squareFib.iteratorValue(iterator)) // expect: 0
+System.print(squareFib.iteratorValue(iterator)) // expect: 0
 
 iterator = squareFib.iterate(iterator)
-IO.print(squareFib.iteratorValue(iterator)) // expect: 1
+System.print(squareFib.iteratorValue(iterator)) // expect: 1
 
 iterator = squareFib.iterate(iterator)
-IO.print(squareFib.iteratorValue(iterator)) // expect: 1
+System.print(squareFib.iteratorValue(iterator)) // expect: 1
 
 iterator = squareFib.iterate(iterator)
-IO.print(squareFib.iteratorValue(iterator)) // expect: 4
+System.print(squareFib.iteratorValue(iterator)) // expect: 4
 
 iterator = squareFib.iterate(iterator)
-IO.print(squareFib.iteratorValue(iterator)) // expect: 9
+System.print(squareFib.iteratorValue(iterator)) // expect: 9
diff --git a/test/core/sequence/to_list.wren b/test/core/sequence/to_list.wren
index cdaf96ff..c92e13b8 100644
--- a/test/core/sequence/to_list.wren
+++ b/test/core/sequence/to_list.wren
@@ -10,4 +10,4 @@ class TestSequence is Sequence {
   iteratorValue(iterator) { iterator }
 }
 
-IO.print(TestSequence.new().toList) // expect: [1, 2, 3]
+System.print(TestSequence.new().toList) // expect: [1, 2, 3]
diff --git a/test/core/sequence/where.wren b/test/core/sequence/where.wren
index c40176fd..27e0e78b 100644
--- a/test/core/sequence/where.wren
+++ b/test/core/sequence/where.wren
@@ -29,14 +29,14 @@ class Fib is Sequence {
 var largeFibs = Fib.new().where {|fib| fib > 100 }
 var iterator = null
 
-IO.print(largeFibs is Sequence) // expect: true
-IO.print(largeFibs) // expect: instance of WhereSequence
+System.print(largeFibs is Sequence) // expect: true
+System.print(largeFibs) // expect: instance of WhereSequence
 
 iterator = largeFibs.iterate(iterator)
-IO.print(largeFibs.iteratorValue(iterator)) // expect: 144
+System.print(largeFibs.iteratorValue(iterator)) // expect: 144
 
 iterator = largeFibs.iterate(iterator)
-IO.print(largeFibs.iteratorValue(iterator)) // expect: 233
+System.print(largeFibs.iteratorValue(iterator)) // expect: 233
 
 iterator = largeFibs.iterate(iterator)
-IO.print(largeFibs.iteratorValue(iterator)) // expect: 377
+System.print(largeFibs.iteratorValue(iterator)) // expect: 377
diff --git a/test/core/string/bytes.wren b/test/core/string/bytes.wren
index f225a81f..b7dad585 100644
--- a/test/core/string/bytes.wren
+++ b/test/core/string/bytes.wren
@@ -3,4 +3,4 @@
 // Chars: sø mé ஃ  thî ng
 var s = "søméஃthîng"
 
-IO.print(s.bytes is StringByteSequence) // expect: true
+System.print(s.bytes is StringByteSequence) // expect: true
diff --git a/test/core/string/concatenation.wren b/test/core/string/concatenation.wren
index cbc696ac..e0da57dd 100644
--- a/test/core/string/concatenation.wren
+++ b/test/core/string/concatenation.wren
@@ -1,4 +1,4 @@
-IO.print("a" + "b") // expect: ab
+System.print("a" + "b") // expect: ab
 
 // 8-bit clean.
-IO.print(("a\0b" + "\0c") == "a\0b\0c")  // expect: true
+System.print(("a\0b" + "\0c") == "a\0b\0c")  // expect: true
diff --git a/test/core/string/concatenation_wrong_arg_type.wren b/test/core/string/concatenation_wrong_arg_type.wren
index 38a5ea01..f7563659 100644
--- a/test/core/string/concatenation_wrong_arg_type.wren
+++ b/test/core/string/concatenation_wrong_arg_type.wren
@@ -1 +1 @@
-IO.print("a" + 123) // expect runtime error: Right operand must be a string.
+System.print("a" + 123) // expect runtime error: Right operand must be a string.
diff --git a/test/core/string/contains.wren b/test/core/string/contains.wren
index 3151c5ef..b0514b86 100644
--- a/test/core/string/contains.wren
+++ b/test/core/string/contains.wren
@@ -1,16 +1,16 @@
-IO.print("".contains(""))              // expect: true
-IO.print("anything".contains(""))      // expect: true
-IO.print("something".contains("meth")) // expect: true
-IO.print("something".contains("some")) // expect: true
-IO.print("something".contains("ing"))  // expect: true
-IO.print("something".contains("math")) // expect: false
+System.print("".contains(""))              // expect: true
+System.print("anything".contains(""))      // expect: true
+System.print("something".contains("meth")) // expect: true
+System.print("something".contains("some")) // expect: true
+System.print("something".contains("ing"))  // expect: true
+System.print("something".contains("math")) // expect: false
 
 // Non-ASCII.
-IO.print("søméthîng".contains("méth"))  // expect: true
-IO.print("søméthîng".contains("meth")) // expect: false
+System.print("søméthîng".contains("méth"))  // expect: true
+System.print("søméthîng".contains("meth")) // expect: false
 
 // 8-bit clean.
-IO.print("a\0b\0c".contains("\0")) // expect: true
-IO.print("a\0b\0c".contains("b")) // expect: true
-IO.print("a\0b\0c".contains("b\0c")) // expect: true
-IO.print("a\0b\0c".contains("bc")) // expect: false
+System.print("a\0b\0c".contains("\0")) // expect: true
+System.print("a\0b\0c".contains("b")) // expect: true
+System.print("a\0b\0c".contains("b\0c")) // expect: true
+System.print("a\0b\0c".contains("bc")) // expect: false
diff --git a/test/core/string/count.wren b/test/core/string/count.wren
index 3213d2d5..b06821b6 100644
--- a/test/core/string/count.wren
+++ b/test/core/string/count.wren
@@ -1,18 +1,18 @@
-IO.print("".count)   // expect: 0
-IO.print("a string".count) // expect: 8
+System.print("".count)   // expect: 0
+System.print("a string".count) // expect: 8
 
 // 8-bit clean.
-IO.print("\0".count)  // expect: 1
-IO.print("a\0b".count)  // expect: 3
-IO.print("\0c".count)  // expect: 2
-IO.print(("a\0b" + "\0c").count)  // expect: 5
+System.print("\0".count)  // expect: 1
+System.print("a\0b".count)  // expect: 3
+System.print("\0c".count)  // expect: 2
+System.print(("a\0b" + "\0c").count)  // expect: 5
 
 // Treats a UTF-8 sequence as a single item.
 //
 // Bytes:           11111
 //        012345678901234
 // Chars: sø mé ஃ  thî ng
-IO.print("søméஃthîng".count) // expect: 10
+System.print("søméஃthîng".count) // expect: 10
 
 // Counts invalid UTF-8 one byte at a time.
-IO.print("\xefok\xf7".count) // expect: 4
+System.print("\xefok\xf7".count) // expect: 4
diff --git a/test/core/string/ends_with.wren b/test/core/string/ends_with.wren
index 6fd81c29..9a2177f5 100644
--- a/test/core/string/ends_with.wren
+++ b/test/core/string/ends_with.wren
@@ -1,15 +1,15 @@
-IO.print("abcd".endsWith("cd")) // expect: true
-IO.print("abcd".endsWith("abcde")) // expect: false
-IO.print("abcd".endsWith("abcd")) // expect: true
-IO.print("abcd".endsWith("f")) // expect: false
-IO.print("abcd".endsWith("")) // expect: true
+System.print("abcd".endsWith("cd")) // expect: true
+System.print("abcd".endsWith("abcde")) // expect: false
+System.print("abcd".endsWith("abcd")) // expect: true
+System.print("abcd".endsWith("f")) // expect: false
+System.print("abcd".endsWith("")) // expect: true
 
 // Non-ASCII.
-IO.print("søméthîng".endsWith("thîng"))  // expect: true
-IO.print("søméthîng".endsWith("thing")) // expect: false
+System.print("søméthîng".endsWith("thîng"))  // expect: true
+System.print("søméthîng".endsWith("thing")) // expect: false
 
 // 8-bit clean.
-IO.print("a\0b\0c".endsWith("\0"))  // expect: false
-IO.print("a\0b\0c".endsWith("c"))  // expect: true
-IO.print("a\0b\0c".endsWith("\0c"))  // expect: true
-IO.print("a\0b\0c".endsWith("\0b"))  // expect: false
+System.print("a\0b\0c".endsWith("\0"))  // expect: false
+System.print("a\0b\0c".endsWith("c"))  // expect: true
+System.print("a\0b\0c".endsWith("\0c"))  // expect: true
+System.print("a\0b\0c".endsWith("\0b"))  // expect: false
diff --git a/test/core/string/ends_with_invalid_arg.wren b/test/core/string/ends_with_invalid_arg.wren
index f7c75fd2..4b729e3b 100644
--- a/test/core/string/ends_with_invalid_arg.wren
+++ b/test/core/string/ends_with_invalid_arg.wren
@@ -1 +1 @@
-IO.print("abcd".endsWith(null)) // expect runtime error: Argument must be a string.
\ No newline at end of file
+System.print("abcd".endsWith(null)) // expect runtime error: Argument must be a string.
\ No newline at end of file
diff --git a/test/core/string/equality.wren b/test/core/string/equality.wren
index 56ae4800..0715ea76 100644
--- a/test/core/string/equality.wren
+++ b/test/core/string/equality.wren
@@ -1,28 +1,28 @@
-IO.print("" == "")          // expect: true
-IO.print("abcd" == "abcd")  // expect: true
-IO.print("abcd" == "d")     // expect: false
-IO.print("e" == "abcd")     // expect: false
-IO.print("" == "abcd")      // expect: false
+System.print("" == "")          // expect: true
+System.print("abcd" == "abcd")  // expect: true
+System.print("abcd" == "d")     // expect: false
+System.print("e" == "abcd")     // expect: false
+System.print("" == "abcd")      // expect: false
 
 // Not equal to other types.
-IO.print("1" == 1)        // expect: false
-IO.print("true" == true)  // expect: false
+System.print("1" == 1)        // expect: false
+System.print("true" == true)  // expect: false
 
-IO.print("" != "")          // expect: false
-IO.print("abcd" != "abcd")  // expect: false
-IO.print("abcd" != "d")     // expect: true
-IO.print("e" != "abcd")     // expect: true
-IO.print("" != "abcd")      // expect: true
+System.print("" != "")          // expect: false
+System.print("abcd" != "abcd")  // expect: false
+System.print("abcd" != "d")     // expect: true
+System.print("e" != "abcd")     // expect: true
+System.print("" != "abcd")      // expect: true
 
 // Not equal to other types.
-IO.print("1" != 1)        // expect: true
-IO.print("true" != true)  // expect: true
+System.print("1" != 1)        // expect: true
+System.print("true" != true)  // expect: true
 
 // Non-ASCII.
-IO.print("vålue" == "value") // expect: false
-IO.print("vålue" == "vålue") // expect: true
+System.print("vålue" == "value") // expect: false
+System.print("vålue" == "vålue") // expect: true
 
 // 8-bit clean.
-IO.print("a\0b\0c" == "a") // expect: false
-IO.print("a\0b\0c" == "abc") // expect: false
-IO.print("a\0b\0c" == "a\0b\0c") // expect: true
+System.print("a\0b\0c" == "a") // expect: false
+System.print("a\0b\0c" == "abc") // expect: false
+System.print("a\0b\0c" == "a\0b\0c") // expect: true
diff --git a/test/core/string/from_code_point.wren b/test/core/string/from_code_point.wren
index b61c8c73..5b9f8761 100644
--- a/test/core/string/from_code_point.wren
+++ b/test/core/string/from_code_point.wren
@@ -1,5 +1,5 @@
-IO.print(String.fromCodePoint(65))   // expect: A
-IO.print(String.fromCodePoint(164))   // expect: ¤
-IO.print(String.fromCodePoint(398))   // expect: Ǝ
-IO.print(String.fromCodePoint(8225))   // expect: ‡
-IO.print(String.fromCodePoint(0x254b))   // expect: ╋
+System.print(String.fromCodePoint(65))   // expect: A
+System.print(String.fromCodePoint(164))   // expect: ¤
+System.print(String.fromCodePoint(398))   // expect: Ǝ
+System.print(String.fromCodePoint(8225))   // expect: ‡
+System.print(String.fromCodePoint(0x254b))   // expect: ╋
diff --git a/test/core/string/from_code_point_not_int.wren b/test/core/string/from_code_point_not_int.wren
index 8ee9e513..78c05201 100644
--- a/test/core/string/from_code_point_not_int.wren
+++ b/test/core/string/from_code_point_not_int.wren
@@ -1 +1 @@
-IO.print(String.fromCodePoint(12.34))   // expect runtime error: Code point must be an integer.
+System.print(String.fromCodePoint(12.34))   // expect runtime error: Code point must be an integer.
diff --git a/test/core/string/from_code_point_not_num.wren b/test/core/string/from_code_point_not_num.wren
index 51daa10f..eaa386da 100644
--- a/test/core/string/from_code_point_not_num.wren
+++ b/test/core/string/from_code_point_not_num.wren
@@ -1 +1 @@
-IO.print(String.fromCodePoint("not num"))   // expect runtime error: Code point must be a number.
+System.print(String.fromCodePoint("not num"))   // expect runtime error: Code point must be a number.
diff --git a/test/core/string/from_code_point_too_large.wren b/test/core/string/from_code_point_too_large.wren
index b213be62..9a9282c5 100644
--- a/test/core/string/from_code_point_too_large.wren
+++ b/test/core/string/from_code_point_too_large.wren
@@ -1,3 +1,3 @@
 // UTF-8 mandates that only values up to 10ffff can be encoded.
 // See: http://tools.ietf.org/html/rfc3629
-IO.print(String.fromCodePoint(0x10ffff + 1))   // expect runtime error: Code point cannot be greater than 0x10ffff.
+System.print(String.fromCodePoint(0x10ffff + 1))   // expect runtime error: Code point cannot be greater than 0x10ffff.
diff --git a/test/core/string/from_code_point_too_small.wren b/test/core/string/from_code_point_too_small.wren
index af4a08c6..5a5eee70 100644
--- a/test/core/string/from_code_point_too_small.wren
+++ b/test/core/string/from_code_point_too_small.wren
@@ -1 +1 @@
-IO.print(String.fromCodePoint(-1))   // expect runtime error: Code point cannot be negative.
+System.print(String.fromCodePoint(-1))   // expect runtime error: Code point cannot be negative.
diff --git a/test/core/string/index_of.wren b/test/core/string/index_of.wren
index 18544278..22fb8f79 100644
--- a/test/core/string/index_of.wren
+++ b/test/core/string/index_of.wren
@@ -1,24 +1,24 @@
-IO.print("abcd".indexOf("")) // expect: 0
-IO.print("abcd".indexOf("cd")) // expect: 2
-IO.print("abcd".indexOf("a")) // expect: 0
-IO.print("abcd".indexOf("abcd")) // expect: 0
-IO.print("abcd".indexOf("abcde")) // expect: -1
-IO.print("abab".indexOf("ab")) // expect: 0
+System.print("abcd".indexOf("")) // expect: 0
+System.print("abcd".indexOf("cd")) // expect: 2
+System.print("abcd".indexOf("a")) // expect: 0
+System.print("abcd".indexOf("abcd")) // expect: 0
+System.print("abcd".indexOf("abcde")) // expect: -1
+System.print("abab".indexOf("ab")) // expect: 0
 
 // More complex cases.
-IO.print("abcdefabcdefg".indexOf("defg")) // expect: 9
-IO.print("abcdabcdabcd".indexOf("dab")) // expect: 3
-IO.print("abcdabcdabcdabcd".indexOf("dabcdabc")) // expect: 3
-IO.print("abcdefg".indexOf("abcdef!")) // expect: -1
+System.print("abcdefabcdefg".indexOf("defg")) // expect: 9
+System.print("abcdabcdabcd".indexOf("dab")) // expect: 3
+System.print("abcdabcdabcdabcd".indexOf("dabcdabc")) // expect: 3
+System.print("abcdefg".indexOf("abcdef!")) // expect: -1
 
 // Non-ASCII. Note that it returns byte indices, not code points.
-IO.print("søméஃthîng".indexOf("e")) // expect: -1
-IO.print("søméஃthîng".indexOf("m")) // expect: 3
-IO.print("søméஃthîng".indexOf("thî")) // expect: 9
+System.print("søméஃthîng".indexOf("e")) // expect: -1
+System.print("søméஃthîng".indexOf("m")) // expect: 3
+System.print("søméஃthîng".indexOf("thî")) // expect: 9
 
 // 8-bit clean.
-IO.print("a\0b\0c".indexOf("\0")) // expect: 1
-IO.print("a\0b\0c".indexOf("a")) // expect: 0
-IO.print("a\0b\0c".indexOf("b\0c")) // expect: 2
-IO.print("a\0b\0c".indexOf("a\0b\0c\0d")) // expect: -1
-IO.print("a\0b\0a\0b".indexOf("a\0b")) // expect: 0
+System.print("a\0b\0c".indexOf("\0")) // expect: 1
+System.print("a\0b\0c".indexOf("a")) // expect: 0
+System.print("a\0b\0c".indexOf("b\0c")) // expect: 2
+System.print("a\0b\0c".indexOf("a\0b\0c\0d")) // expect: -1
+System.print("a\0b\0a\0b".indexOf("a\0b")) // expect: 0
diff --git a/test/core/string/index_of_invalid_arg.wren b/test/core/string/index_of_invalid_arg.wren
index 5d9393c5..d51c6af7 100644
--- a/test/core/string/index_of_invalid_arg.wren
+++ b/test/core/string/index_of_invalid_arg.wren
@@ -1 +1 @@
-IO.print("abcd".indexOf(null)) // expect runtime error: Argument must be a string.
+System.print("abcd".indexOf(null)) // expect runtime error: Argument must be a string.
diff --git a/test/core/string/iterate.wren b/test/core/string/iterate.wren
index 6fd3ce3b..012db13b 100644
--- a/test/core/string/iterate.wren
+++ b/test/core/string/iterate.wren
@@ -1,29 +1,29 @@
 var s = "abçd"
-IO.print(s.iterate(null)) // expect: 0
-IO.print(s.iterate(0)) // expect: 1
-IO.print(s.iterate(1)) // expect: 2
+System.print(s.iterate(null)) // expect: 0
+System.print(s.iterate(0)) // expect: 1
+System.print(s.iterate(1)) // expect: 2
 // Skip 3 because that's the middle of the ç sequence.
-IO.print(s.iterate(2)) // expect: 4
+System.print(s.iterate(2)) // expect: 4
 // Iterating from the middle of a UTF-8 sequence goes to the next one.
-IO.print(s.iterate(3)) // expect: 4
-IO.print(s.iterate(4)) // expect: false
+System.print(s.iterate(3)) // expect: 4
+System.print(s.iterate(4)) // expect: false
 
 // Out of bounds.
-IO.print(s.iterate(123)) // expect: false
-IO.print(s.iterate(-1)) // expect: false
+System.print(s.iterate(123)) // expect: false
+System.print(s.iterate(-1)) // expect: false
 
 // Nothing to iterate in an empty string.
-IO.print("".iterate(null)) // expect: false
+System.print("".iterate(null)) // expect: false
 
 // 8-bit clean.
-IO.print("a\0b\0c".iterate(null)) // expect: 0
-IO.print("a\0b\0c".iterate(0)) // expect: 1
-IO.print("a\0b\0c".iterate(1)) // expect: 2
-IO.print("a\0b\0c".iterate(2)) // expect: 3
-IO.print("a\0b\0c".iterate(3)) // expect: 4
-IO.print("a\0b\0c".iterate(4)) // expect: false
+System.print("a\0b\0c".iterate(null)) // expect: 0
+System.print("a\0b\0c".iterate(0)) // expect: 1
+System.print("a\0b\0c".iterate(1)) // expect: 2
+System.print("a\0b\0c".iterate(2)) // expect: 3
+System.print("a\0b\0c".iterate(3)) // expect: 4
+System.print("a\0b\0c".iterate(4)) // expect: false
 
 // Iterates over invalid UTF-8 one byte at a time.
-IO.print("\xef\xf7".iterate(null)) // expect: 0
-IO.print("\xef\xf7".iterate(0)) // expect: 1
-IO.print("\xef\xf7".iterate(1)) // expect: false
+System.print("\xef\xf7".iterate(null)) // expect: 0
+System.print("\xef\xf7".iterate(0)) // expect: 1
+System.print("\xef\xf7".iterate(1)) // expect: false
diff --git a/test/core/string/iterator_value.wren b/test/core/string/iterator_value.wren
index 85838310..7ae2669b 100644
--- a/test/core/string/iterator_value.wren
+++ b/test/core/string/iterator_value.wren
@@ -1,19 +1,19 @@
 var s = "abçd"
-IO.print(s.iteratorValue(0)) // expect: a
-IO.print(s.iteratorValue(1)) // expect: b
-IO.print(s.iteratorValue(2)) // expect: ç
+System.print(s.iteratorValue(0)) // expect: a
+System.print(s.iteratorValue(1)) // expect: b
+System.print(s.iteratorValue(2)) // expect: ç
 // Iterator value in middle of UTF sequence is the unencoded byte.
-IO.print(s.iteratorValue(3) == "\xa7") // expect: true
-IO.print(s.iteratorValue(4)) // expect: d
+System.print(s.iteratorValue(3) == "\xa7") // expect: true
+System.print(s.iteratorValue(4)) // expect: d
 
 // 8-bit clean.
 var t = "a\0b\0c"
-IO.print(t.iteratorValue(0) == "a") // expect: true
-IO.print(t.iteratorValue(1) == "\0") // expect: true
-IO.print(t.iteratorValue(2) == "b") // expect: true
-IO.print(t.iteratorValue(3) == "\0") // expect: true
-IO.print(t.iteratorValue(4) == "c") // expect: true
+System.print(t.iteratorValue(0) == "a") // expect: true
+System.print(t.iteratorValue(1) == "\0") // expect: true
+System.print(t.iteratorValue(2) == "b") // expect: true
+System.print(t.iteratorValue(3) == "\0") // expect: true
+System.print(t.iteratorValue(4) == "c") // expect: true
 
 // Returns single byte strings for invalid UTF-8 sequences.
-IO.print("\xef\xf7".iteratorValue(0) == "\xef") // expect: true
-IO.print("\xef\xf7".iteratorValue(1) == "\xf7") // expect: true
+System.print("\xef\xf7".iteratorValue(0) == "\xef") // expect: true
+System.print("\xef\xf7".iteratorValue(1) == "\xf7") // expect: true
diff --git a/test/core/string/join.wren b/test/core/string/join.wren
index 19a8f215..7676cc41 100644
--- a/test/core/string/join.wren
+++ b/test/core/string/join.wren
@@ -1,10 +1,10 @@
 var str = "string"
 
-IO.print(str.join("") == str) // expect: true
+System.print(str.join("") == str) // expect: true
 
-IO.print(str.join(", ")) // expect: s, t, r, i, n, g
+System.print(str.join(", ")) // expect: s, t, r, i, n, g
 
 // 8-bit clean.
 var ing = "a\0b\0c"
-IO.print(ing.join("") == ing) // expect: true
-IO.print(ing.join(", ") == "a, \0, b, \0, c") // expect: true
+System.print(ing.join("") == ing) // expect: true
+System.print(ing.join(", ") == "a, \0, b, \0, c") // expect: true
diff --git a/test/core/string/not.wren b/test/core/string/not.wren
index 03e48e15..889a666a 100644
--- a/test/core/string/not.wren
+++ b/test/core/string/not.wren
@@ -1,2 +1,2 @@
-IO.print(!"s") // expect: false
-IO.print(!"") // expect: false
+System.print(!"s") // expect: false
+System.print(!"") // expect: false
diff --git a/test/core/string/starts_with.wren b/test/core/string/starts_with.wren
index 1b22e669..6d6944ac 100644
--- a/test/core/string/starts_with.wren
+++ b/test/core/string/starts_with.wren
@@ -1,14 +1,14 @@
-IO.print("abcd".startsWith("cd")) // expect: false
-IO.print("abcd".startsWith("a")) // expect: true
-IO.print("abcd".startsWith("abcd")) // expect: true
-IO.print("abcd".startsWith("abcde")) // expect: false
-IO.print("abcd".startsWith("")) // expect: true
+System.print("abcd".startsWith("cd")) // expect: false
+System.print("abcd".startsWith("a")) // expect: true
+System.print("abcd".startsWith("abcd")) // expect: true
+System.print("abcd".startsWith("abcde")) // expect: false
+System.print("abcd".startsWith("")) // expect: true
 
 // Non-ASCII.
-IO.print("søméthîng".startsWith("sømé"))  // expect: true
-IO.print("søméthîng".startsWith("some")) // expect: false
+System.print("søméthîng".startsWith("sømé"))  // expect: true
+System.print("søméthîng".startsWith("some")) // expect: false
 
 // 8-bit clean.
-IO.print("a\0b\0c".startsWith("a"))  // expect: true
-IO.print("a\0b\0c".startsWith("a\0"))  // expect: true
-IO.print("a\0b\0c".startsWith("b\0"))  // expect: false
+System.print("a\0b\0c".startsWith("a"))  // expect: true
+System.print("a\0b\0c".startsWith("a\0"))  // expect: true
+System.print("a\0b\0c".startsWith("b\0"))  // expect: false
diff --git a/test/core/string/starts_with_invalid_arg.wren b/test/core/string/starts_with_invalid_arg.wren
index 7863aebc..7db1e71e 100644
--- a/test/core/string/starts_with_invalid_arg.wren
+++ b/test/core/string/starts_with_invalid_arg.wren
@@ -1 +1 @@
-IO.print("abcd".startsWith(null)) // expect runtime error: Argument must be a string.
+System.print("abcd".startsWith(null)) // expect runtime error: Argument must be a string.
diff --git a/test/core/string/subscript.wren b/test/core/string/subscript.wren
index 97998efe..9c4dd5df 100644
--- a/test/core/string/subscript.wren
+++ b/test/core/string/subscript.wren
@@ -1,46 +1,46 @@
 // Returns characters (as strings).
-IO.print("abcd"[0]) // expect: a
-IO.print("abcd"[1]) // expect: b
-IO.print("abcd"[2]) // expect: c
-IO.print("abcd"[3]) // expect: d
+System.print("abcd"[0]) // expect: a
+System.print("abcd"[1]) // expect: b
+System.print("abcd"[2]) // expect: c
+System.print("abcd"[3]) // expect: d
 
 // Allows indexing backwards from the end.
-IO.print("abcd"[-4]) // expect: a
-IO.print("abcd"[-3]) // expect: b
-IO.print("abcd"[-2]) // expect: c
-IO.print("abcd"[-1]) // expect: d
+System.print("abcd"[-4]) // expect: a
+System.print("abcd"[-3]) // expect: b
+System.print("abcd"[-2]) // expect: c
+System.print("abcd"[-1]) // expect: d
 
 // Regression: Make sure the string's internal buffer size is correct.
-IO.print("abcd"[1] == "b") // expect: true
+System.print("abcd"[1] == "b") // expect: true
 
 // Indexes by byte, not code point.
 //
 // Bytes:           11111
 //        012345678901234
 // Chars: sø mé ஃ  thî ng
-IO.print("søméஃthîng"[0]) // expect: s
-IO.print("søméஃthîng"[1]) // expect: ø
-IO.print("søméஃthîng"[3]) // expect: m
-IO.print("søméஃthîng"[6]) // expect: ஃ
-IO.print("søméஃthîng"[10]) // expect: h
-IO.print("søméஃthîng"[-1]) // expect: g
-IO.print("søméஃthîng"[-2]) // expect: n
-IO.print("søméஃthîng"[-4]) // expect: î
+System.print("søméஃthîng"[0]) // expect: s
+System.print("søméஃthîng"[1]) // expect: ø
+System.print("søméஃthîng"[3]) // expect: m
+System.print("søméஃthîng"[6]) // expect: ஃ
+System.print("søméஃthîng"[10]) // expect: h
+System.print("søméஃthîng"[-1]) // expect: g
+System.print("søméஃthîng"[-2]) // expect: n
+System.print("søméஃthîng"[-4]) // expect: î
 
 // If the subscript is in the middle of a UTF-8 sequence, return the raw byte.
-IO.print("søméஃthîng"[2] == "\xb8") // expect: true
-IO.print("søméஃthîng"[7] == "\xae") // expect: true
-IO.print("søméஃthîng"[8] == "\x83") // expect: true
-IO.print("søméஃ"[-1] == "\x83") // expect: true
-IO.print("søméஃ"[-2] == "\xae") // expect: true
+System.print("søméஃthîng"[2] == "\xb8") // expect: true
+System.print("søméஃthîng"[7] == "\xae") // expect: true
+System.print("søméஃthîng"[8] == "\x83") // expect: true
+System.print("søméஃ"[-1] == "\x83") // expect: true
+System.print("søméஃ"[-2] == "\xae") // expect: true
 
 // 8-bit clean.
-IO.print("a\0b\0c"[0] == "a") // expect: true
-IO.print("a\0b\0c"[1] == "\0") // expect: true
-IO.print("a\0b\0c"[2] == "b") // expect: true
-IO.print("a\0b\0c"[3] == "\0") // expect: true
-IO.print("a\0b\0c"[4] == "c") // expect: true
+System.print("a\0b\0c"[0] == "a") // expect: true
+System.print("a\0b\0c"[1] == "\0") // expect: true
+System.print("a\0b\0c"[2] == "b") // expect: true
+System.print("a\0b\0c"[3] == "\0") // expect: true
+System.print("a\0b\0c"[4] == "c") // expect: true
 
 // Returns single byte strings for invalid UTF-8 sequences.
-IO.print("\xef\xf7"[0] == "\xef") // expect: true
-IO.print("\xef\xf7"[1] == "\xf7") // expect: true
+System.print("\xef\xf7"[0] == "\xef") // expect: true
+System.print("\xef\xf7"[1] == "\xf7") // expect: true
diff --git a/test/core/string/subscript_range.wren b/test/core/string/subscript_range.wren
index 75277e81..43ff4b34 100644
--- a/test/core/string/subscript_range.wren
+++ b/test/core/string/subscript_range.wren
@@ -1,49 +1,49 @@
 var string = "abcde"
-IO.print(string[0..0]) // expect: a
-IO.print(string[1...1] == "") // expect: true
-IO.print(string[1..2]) // expect: bc
-IO.print(string[1...2]) // expect: b
-IO.print(string[2..4]) // expect: cde
-IO.print(string[2...5]) // expect: cde
+System.print(string[0..0]) // expect: a
+System.print(string[1...1] == "") // expect: true
+System.print(string[1..2]) // expect: bc
+System.print(string[1...2]) // expect: b
+System.print(string[2..4]) // expect: cde
+System.print(string[2...5]) // expect: cde
 
 // A backwards range reverses.
-IO.print(string[3..1]) // expect: dcb
-IO.print(string[3...1]) // expect: dc
-IO.print(string[3...3] == "") // expect: true
+System.print(string[3..1]) // expect: dcb
+System.print(string[3...1]) // expect: dc
+System.print(string[3...3] == "") // expect: true
 
 // Negative ranges index from the end.
-IO.print(string[-5..-2]) // expect: abcd
-IO.print(string[-5...-2]) // expect: abc
-IO.print(string[-3..-5]) // expect: cba
-IO.print(string[-3...-6]) // expect: cba
+System.print(string[-5..-2]) // expect: abcd
+System.print(string[-5...-2]) // expect: abc
+System.print(string[-3..-5]) // expect: cba
+System.print(string[-3...-6]) // expect: cba
 
 // Half-negative ranges are treated like the negative value is fixed before
 // walking the range.
-IO.print(string[-5..3]) // expect: abcd
-IO.print(string[-3...5]) // expect: cde
-IO.print(string[-2..1]) // expect: dcb
-IO.print(string[-2...0]) // expect: dcb
+System.print(string[-5..3]) // expect: abcd
+System.print(string[-3...5]) // expect: cde
+System.print(string[-2..1]) // expect: dcb
+System.print(string[-2...0]) // expect: dcb
 
-IO.print(string[1..-2]) // expect: bcd
-IO.print(string[2...-1]) // expect: cd
-IO.print(string[4..-5]) // expect: edcba
-IO.print(string[3...-6]) // expect: dcba
+System.print(string[1..-2]) // expect: bcd
+System.print(string[2...-1]) // expect: cd
+System.print(string[4..-5]) // expect: edcba
+System.print(string[3...-6]) // expect: dcba
 
 // An empty range at zero is allowed on an empty string.
-IO.print(""[0...0] == "") // expect: true
-IO.print(""[0..-1] == "") // expect: true
+System.print(""[0...0] == "") // expect: true
+System.print(""[0..-1] == "") // expect: true
 
 // Indexes by byte, not code point.
 //
 // Bytes:           11111
 //        012345678901234
 // Chars: sø mé ஃ  thî ng
-IO.print("søméஃthîng"[0..3]) // expect: søm
-IO.print("søméஃthîng"[3...10]) // expect: méஃt
+System.print("søméஃthîng"[0..3]) // expect: søm
+System.print("søméஃthîng"[3...10]) // expect: méஃt
 
 // Only includes sequences whose first byte is in the range.
-IO.print("søméஃthîng"[2..6]) // expect: méஃ
-IO.print("søméஃthîng"[2...6]) // expect: mé
-IO.print("søméஃthîng"[2...7]) // expect: méஃ
+System.print("søméஃthîng"[2..6]) // expect: méஃ
+System.print("søméஃthîng"[2...6]) // expect: mé
+System.print("søméஃthîng"[2...7]) // expect: méஃ
 
 // TODO: Strings including invalid UTF-8.
diff --git a/test/core/string/to_string.wren b/test/core/string/to_string.wren
index 16d60d49..6fefb0e5 100644
--- a/test/core/string/to_string.wren
+++ b/test/core/string/to_string.wren
@@ -1,7 +1,7 @@
-IO.print("".toString == "") // expect: true
-IO.print("blah".toString == "blah") // expect: true
+System.print("".toString == "") // expect: true
+System.print("blah".toString == "blah") // expect: true
 
 // 8-bit clean.
-IO.print("a\0b\0c".toString == "a\0b\0c") // expect: true
-IO.print("a\0b\0c".toString == "a") // expect: false
-IO.print("a\0b\0c".toString) // expect: a
+System.print("a\0b\0c".toString == "a\0b\0c") // expect: true
+System.print("a\0b\0c".toString == "a") // expect: false
+System.print("a\0b\0c".toString) // expect: a
diff --git a/test/core/string/type.wren b/test/core/string/type.wren
index 9af9bdf1..351333cd 100644
--- a/test/core/string/type.wren
+++ b/test/core/string/type.wren
@@ -1,4 +1,4 @@
-IO.print("s" is String)      // expect: true
-IO.print("s" is Object)      // expect: true
-IO.print("s" is Num)         // expect: false
-IO.print("s".type == String) // expect: true
+System.print("s" is String)      // expect: true
+System.print("s" is Object)      // expect: true
+System.print("s" is Num)         // expect: false
+System.print("s".type == String) // expect: true
diff --git a/test/core/string_byte_sequence/count.wren b/test/core/string_byte_sequence/count.wren
index 822d0f98..fc7e862d 100644
--- a/test/core/string_byte_sequence/count.wren
+++ b/test/core/string_byte_sequence/count.wren
@@ -1,15 +1,15 @@
 // Simple.
-IO.print("".bytes.count) // expect: 0
-IO.print("123".bytes.count) // expect: 3
+System.print("".bytes.count) // expect: 0
+System.print("123".bytes.count) // expect: 3
 
 // UTF-8.
 // Bytes:
 //        123456789
 // Chars: sø mé ஃ
-IO.print("søméஃ".bytes.count) // expect: 9
+System.print("søméஃ".bytes.count) // expect: 9
 
 // Null bytes.
-IO.print("\0\0\0".bytes.count) // expect: 3
+System.print("\0\0\0".bytes.count) // expect: 3
 
 // Invalid UTF-8.
-IO.print("\xef\xf7".bytes.count) // expect: 2
+System.print("\xef\xf7".bytes.count) // expect: 2
diff --git a/test/core/string_byte_sequence/iterate.wren b/test/core/string_byte_sequence/iterate.wren
index 650a61d4..b784cfdb 100644
--- a/test/core/string_byte_sequence/iterate.wren
+++ b/test/core/string_byte_sequence/iterate.wren
@@ -3,19 +3,19 @@
 // Chars: sø mé ஃ
 var bytes = "søméஃ".bytes
 
-IO.print(bytes.iterate(null)) // expect: 0
-IO.print("".bytes.iterate(null)) // expect: false
+System.print(bytes.iterate(null)) // expect: 0
+System.print("".bytes.iterate(null)) // expect: false
 
-IO.print(bytes.iterate(0)) // expect: 1
-IO.print(bytes.iterate(1)) // expect: 2
-IO.print(bytes.iterate(2)) // expect: 3
-IO.print(bytes.iterate(3)) // expect: 4
-IO.print(bytes.iterate(4)) // expect: 5
-IO.print(bytes.iterate(5)) // expect: 6
-IO.print(bytes.iterate(6)) // expect: 7
-IO.print(bytes.iterate(7)) // expect: 8
-IO.print(bytes.iterate(8)) // expect: false
+System.print(bytes.iterate(0)) // expect: 1
+System.print(bytes.iterate(1)) // expect: 2
+System.print(bytes.iterate(2)) // expect: 3
+System.print(bytes.iterate(3)) // expect: 4
+System.print(bytes.iterate(4)) // expect: 5
+System.print(bytes.iterate(5)) // expect: 6
+System.print(bytes.iterate(6)) // expect: 7
+System.print(bytes.iterate(7)) // expect: 8
+System.print(bytes.iterate(8)) // expect: false
 
 // Out of bounds.
-IO.print(bytes.iterate(123)) // expect: false
-IO.print(bytes.iterate(-1)) // expect: false
+System.print(bytes.iterate(123)) // expect: false
+System.print(bytes.iterate(-1)) // expect: false
diff --git a/test/core/string_byte_sequence/iterator_value.wren b/test/core/string_byte_sequence/iterator_value.wren
index 544d3869..329589ae 100644
--- a/test/core/string_byte_sequence/iterator_value.wren
+++ b/test/core/string_byte_sequence/iterator_value.wren
@@ -3,22 +3,22 @@
 // Chars: sø mé ஃ
 var bytes = "søméஃ".bytes
 
-IO.print(bytes.iteratorValue(0)) // expect: 115
-IO.print(bytes.iteratorValue(1)) // expect: 195
-IO.print(bytes.iteratorValue(2)) // expect: 184
-IO.print(bytes.iteratorValue(3)) // expect: 109
-IO.print(bytes.iteratorValue(4)) // expect: 195
-IO.print(bytes.iteratorValue(5)) // expect: 169
-IO.print(bytes.iteratorValue(6)) // expect: 224
-IO.print(bytes.iteratorValue(7)) // expect: 174
-IO.print(bytes.iteratorValue(8)) // expect: 131
+System.print(bytes.iteratorValue(0)) // expect: 115
+System.print(bytes.iteratorValue(1)) // expect: 195
+System.print(bytes.iteratorValue(2)) // expect: 184
+System.print(bytes.iteratorValue(3)) // expect: 109
+System.print(bytes.iteratorValue(4)) // expect: 195
+System.print(bytes.iteratorValue(5)) // expect: 169
+System.print(bytes.iteratorValue(6)) // expect: 224
+System.print(bytes.iteratorValue(7)) // expect: 174
+System.print(bytes.iteratorValue(8)) // expect: 131
 
-IO.print(bytes.iteratorValue(-9)) // expect: 115
-IO.print(bytes.iteratorValue(-8)) // expect: 195
-IO.print(bytes.iteratorValue(-7)) // expect: 184
-IO.print(bytes.iteratorValue(-6)) // expect: 109
-IO.print(bytes.iteratorValue(-5)) // expect: 195
-IO.print(bytes.iteratorValue(-4)) // expect: 169
-IO.print(bytes.iteratorValue(-3)) // expect: 224
-IO.print(bytes.iteratorValue(-2)) // expect: 174
-IO.print(bytes.iteratorValue(-1)) // expect: 131
+System.print(bytes.iteratorValue(-9)) // expect: 115
+System.print(bytes.iteratorValue(-8)) // expect: 195
+System.print(bytes.iteratorValue(-7)) // expect: 184
+System.print(bytes.iteratorValue(-6)) // expect: 109
+System.print(bytes.iteratorValue(-5)) // expect: 195
+System.print(bytes.iteratorValue(-4)) // expect: 169
+System.print(bytes.iteratorValue(-3)) // expect: 224
+System.print(bytes.iteratorValue(-2)) // expect: 174
+System.print(bytes.iteratorValue(-1)) // expect: 131
diff --git a/test/core/string_byte_sequence/subscript.wren b/test/core/string_byte_sequence/subscript.wren
index 0e073978..17131581 100644
--- a/test/core/string_byte_sequence/subscript.wren
+++ b/test/core/string_byte_sequence/subscript.wren
@@ -3,22 +3,22 @@
 // Chars: sø mé ஃ
 var bytes = "søméஃ".bytes
 
-IO.print(bytes[0]) // expect: 115
-IO.print(bytes[1]) // expect: 195
-IO.print(bytes[2]) // expect: 184
-IO.print(bytes[3]) // expect: 109
-IO.print(bytes[4]) // expect: 195
-IO.print(bytes[5]) // expect: 169
-IO.print(bytes[6]) // expect: 224
-IO.print(bytes[7]) // expect: 174
-IO.print(bytes[8]) // expect: 131
+System.print(bytes[0]) // expect: 115
+System.print(bytes[1]) // expect: 195
+System.print(bytes[2]) // expect: 184
+System.print(bytes[3]) // expect: 109
+System.print(bytes[4]) // expect: 195
+System.print(bytes[5]) // expect: 169
+System.print(bytes[6]) // expect: 224
+System.print(bytes[7]) // expect: 174
+System.print(bytes[8]) // expect: 131
 
-IO.print(bytes[-9]) // expect: 115
-IO.print(bytes[-8]) // expect: 195
-IO.print(bytes[-7]) // expect: 184
-IO.print(bytes[-6]) // expect: 109
-IO.print(bytes[-5]) // expect: 195
-IO.print(bytes[-4]) // expect: 169
-IO.print(bytes[-3]) // expect: 224
-IO.print(bytes[-2]) // expect: 174
-IO.print(bytes[-1]) // expect: 131
+System.print(bytes[-9]) // expect: 115
+System.print(bytes[-8]) // expect: 195
+System.print(bytes[-7]) // expect: 184
+System.print(bytes[-6]) // expect: 109
+System.print(bytes[-5]) // expect: 195
+System.print(bytes[-4]) // expect: 169
+System.print(bytes[-3]) // expect: 224
+System.print(bytes[-2]) // expect: 174
+System.print(bytes[-1]) // expect: 131
diff --git a/test/core/string_code_point_sequence/count.wren b/test/core/string_code_point_sequence/count.wren
index 4b9c87e3..e90e8b25 100644
--- a/test/core/string_code_point_sequence/count.wren
+++ b/test/core/string_code_point_sequence/count.wren
@@ -1,18 +1,18 @@
-IO.print("".codePoints.count)   // expect: 0
-IO.print("a string".codePoints.count) // expect: 8
+System.print("".codePoints.count)   // expect: 0
+System.print("a string".codePoints.count) // expect: 8
 
 // 8-bit clean.
-IO.print("\0".codePoints.count)  // expect: 1
-IO.print("a\0b".codePoints.count)  // expect: 3
-IO.print("\0c".codePoints.count)  // expect: 2
-IO.print(("a\0b" + "\0c").codePoints.count)  // expect: 5
+System.print("\0".codePoints.count)  // expect: 1
+System.print("a\0b".codePoints.count)  // expect: 3
+System.print("\0c".codePoints.count)  // expect: 2
+System.print(("a\0b" + "\0c").codePoints.count)  // expect: 5
 
 // Treats a UTF-8 sequence as a single item.
 //
 // Bytes:           11111
 //        012345678901234
 // Chars: sø mé ஃ  thî ng
-IO.print("søméஃthîng".codePoints.count) // expect: 10
+System.print("søméஃthîng".codePoints.count) // expect: 10
 
 // Counts invalid UTF-8 one byte at a time.
-IO.print("\xefok\xf7".codePoints.count) // expect: 4
+System.print("\xefok\xf7".codePoints.count) // expect: 4
diff --git a/test/core/string_code_point_sequence/iterate.wren b/test/core/string_code_point_sequence/iterate.wren
index f29db020..fd2eb307 100644
--- a/test/core/string_code_point_sequence/iterate.wren
+++ b/test/core/string_code_point_sequence/iterate.wren
@@ -1,29 +1,29 @@
 var codePoints = "abçd".codePoints
-IO.print(codePoints.iterate(null)) // expect: 0
-IO.print(codePoints.iterate(0)) // expect: 1
-IO.print(codePoints.iterate(1)) // expect: 2
+System.print(codePoints.iterate(null)) // expect: 0
+System.print(codePoints.iterate(0)) // expect: 1
+System.print(codePoints.iterate(1)) // expect: 2
 // Skip 3 because that's the middle of the ç sequence.
-IO.print(codePoints.iterate(2)) // expect: 4
+System.print(codePoints.iterate(2)) // expect: 4
 // Iterating from the middle of a UTF-8 sequence goes to the next one.
-IO.print(codePoints.iterate(3)) // expect: 4
-IO.print(codePoints.iterate(4)) // expect: false
+System.print(codePoints.iterate(3)) // expect: 4
+System.print(codePoints.iterate(4)) // expect: false
 
 // Out of bounds.
-IO.print(codePoints.iterate(123)) // expect: false
-IO.print(codePoints.iterate(-1)) // expect: false
+System.print(codePoints.iterate(123)) // expect: false
+System.print(codePoints.iterate(-1)) // expect: false
 
 // Nothing to iterate in an empty string.
-IO.print("".codePoints.iterate(null)) // expect: false
+System.print("".codePoints.iterate(null)) // expect: false
 
 // 8-bit clean.
-IO.print("a\0b\0c".codePoints.iterate(null)) // expect: 0
-IO.print("a\0b\0c".codePoints.iterate(0)) // expect: 1
-IO.print("a\0b\0c".codePoints.iterate(1)) // expect: 2
-IO.print("a\0b\0c".codePoints.iterate(2)) // expect: 3
-IO.print("a\0b\0c".codePoints.iterate(3)) // expect: 4
-IO.print("a\0b\0c".codePoints.iterate(4)) // expect: false
+System.print("a\0b\0c".codePoints.iterate(null)) // expect: 0
+System.print("a\0b\0c".codePoints.iterate(0)) // expect: 1
+System.print("a\0b\0c".codePoints.iterate(1)) // expect: 2
+System.print("a\0b\0c".codePoints.iterate(2)) // expect: 3
+System.print("a\0b\0c".codePoints.iterate(3)) // expect: 4
+System.print("a\0b\0c".codePoints.iterate(4)) // expect: false
 
 // Iterates over invalid UTF-8 one byte at a time.
-IO.print("\xef\xf7".codePoints.iterate(null)) // expect: 0
-IO.print("\xef\xf7".codePoints.iterate(0)) // expect: 1
-IO.print("\xef\xf7".codePoints.iterate(1)) // expect: false
+System.print("\xef\xf7".codePoints.iterate(null)) // expect: 0
+System.print("\xef\xf7".codePoints.iterate(0)) // expect: 1
+System.print("\xef\xf7".codePoints.iterate(1)) // expect: false
diff --git a/test/core/string_code_point_sequence/iterator_value.wren b/test/core/string_code_point_sequence/iterator_value.wren
index 54af5f1b..46a6d925 100644
--- a/test/core/string_code_point_sequence/iterator_value.wren
+++ b/test/core/string_code_point_sequence/iterator_value.wren
@@ -3,40 +3,40 @@
 // Chars: sø mé ஃ  thî ng
 var codePoints = "søméஃthîng".codePoints
 
-IO.print(codePoints.iteratorValue(0)) // expect: 115
-IO.print(codePoints.iteratorValue(1)) // expect: 248
-IO.print(codePoints.iteratorValue(2)) // expect: -1
-IO.print(codePoints.iteratorValue(3)) // expect: 109
-IO.print(codePoints.iteratorValue(4)) // expect: 233
-IO.print(codePoints.iteratorValue(5)) // expect: -1
-IO.print(codePoints.iteratorValue(6)) // expect: 2947
-IO.print(codePoints.iteratorValue(7)) // expect: -1
-IO.print(codePoints.iteratorValue(8)) // expect: -1
-IO.print(codePoints.iteratorValue(9)) // expect: 116
-IO.print(codePoints.iteratorValue(10)) // expect: 104
-IO.print(codePoints.iteratorValue(11)) // expect: 238
-IO.print(codePoints.iteratorValue(12)) // expect: -1
-IO.print(codePoints.iteratorValue(13)) // expect: 110
-IO.print(codePoints.iteratorValue(14)) // expect: 103
+System.print(codePoints.iteratorValue(0)) // expect: 115
+System.print(codePoints.iteratorValue(1)) // expect: 248
+System.print(codePoints.iteratorValue(2)) // expect: -1
+System.print(codePoints.iteratorValue(3)) // expect: 109
+System.print(codePoints.iteratorValue(4)) // expect: 233
+System.print(codePoints.iteratorValue(5)) // expect: -1
+System.print(codePoints.iteratorValue(6)) // expect: 2947
+System.print(codePoints.iteratorValue(7)) // expect: -1
+System.print(codePoints.iteratorValue(8)) // expect: -1
+System.print(codePoints.iteratorValue(9)) // expect: 116
+System.print(codePoints.iteratorValue(10)) // expect: 104
+System.print(codePoints.iteratorValue(11)) // expect: 238
+System.print(codePoints.iteratorValue(12)) // expect: -1
+System.print(codePoints.iteratorValue(13)) // expect: 110
+System.print(codePoints.iteratorValue(14)) // expect: 103
 
-IO.print(codePoints.iteratorValue(-15)) // expect: 115
-IO.print(codePoints.iteratorValue(-14)) // expect: 248
-IO.print(codePoints.iteratorValue(-13)) // expect: -1
-IO.print(codePoints.iteratorValue(-12)) // expect: 109
-IO.print(codePoints.iteratorValue(-11)) // expect: 233
-IO.print(codePoints.iteratorValue(-10)) // expect: -1
-IO.print(codePoints.iteratorValue(-9)) // expect: 2947
-IO.print(codePoints.iteratorValue(-8)) // expect: -1
-IO.print(codePoints.iteratorValue(-7)) // expect: -1
-IO.print(codePoints.iteratorValue(-6)) // expect: 116
-IO.print(codePoints.iteratorValue(-5)) // expect: 104
-IO.print(codePoints.iteratorValue(-4)) // expect: 238
-IO.print(codePoints.iteratorValue(-3)) // expect: -1
-IO.print(codePoints.iteratorValue(-2)) // expect: 110
-IO.print(codePoints.iteratorValue(-1)) // expect: 103
+System.print(codePoints.iteratorValue(-15)) // expect: 115
+System.print(codePoints.iteratorValue(-14)) // expect: 248
+System.print(codePoints.iteratorValue(-13)) // expect: -1
+System.print(codePoints.iteratorValue(-12)) // expect: 109
+System.print(codePoints.iteratorValue(-11)) // expect: 233
+System.print(codePoints.iteratorValue(-10)) // expect: -1
+System.print(codePoints.iteratorValue(-9)) // expect: 2947
+System.print(codePoints.iteratorValue(-8)) // expect: -1
+System.print(codePoints.iteratorValue(-7)) // expect: -1
+System.print(codePoints.iteratorValue(-6)) // expect: 116
+System.print(codePoints.iteratorValue(-5)) // expect: 104
+System.print(codePoints.iteratorValue(-4)) // expect: 238
+System.print(codePoints.iteratorValue(-3)) // expect: -1
+System.print(codePoints.iteratorValue(-2)) // expect: 110
+System.print(codePoints.iteratorValue(-1)) // expect: 103
 
-IO.print("\0".codePoints.iteratorValue(0)) // expect: 0
+System.print("\0".codePoints.iteratorValue(0)) // expect: 0
 
 // Returns -1 for invalid UTF-8 sequences.
-IO.print("\xef\xf7".codePoints.iteratorValue(0)) // expect: -1
-IO.print("\xef\xf7".codePoints.iteratorValue(1)) // expect: -1
+System.print("\xef\xf7".codePoints.iteratorValue(0)) // expect: -1
+System.print("\xef\xf7".codePoints.iteratorValue(1)) // expect: -1
diff --git a/test/core/string_code_point_sequence/iterator_value_incomplete.wren b/test/core/string_code_point_sequence/iterator_value_incomplete.wren
index ebc59184..fcdab1f9 100644
--- a/test/core/string_code_point_sequence/iterator_value_incomplete.wren
+++ b/test/core/string_code_point_sequence/iterator_value_incomplete.wren
@@ -1,8 +1,8 @@
 // The first byte of a two-octet sequence.
-IO.print("\xc0".codePoints.iteratorValue(0)) // expect: -1
+System.print("\xc0".codePoints.iteratorValue(0)) // expect: -1
 
 // The first byte of a three-octet sequence.
-IO.print("\xe0".codePoints.iteratorValue(0)) // expect: -1
+System.print("\xe0".codePoints.iteratorValue(0)) // expect: -1
 
 // The first two bytes of a three-octet sequence.
-IO.print("\xe0\xae".codePoints.iteratorValue(0)) // expect: -1
+System.print("\xe0\xae".codePoints.iteratorValue(0)) // expect: -1
diff --git a/test/core/string_code_point_sequence/iterator_value_not_int.wren b/test/core/string_code_point_sequence/iterator_value_not_int.wren
index 0f4ed51b..eed2fd92 100644
--- a/test/core/string_code_point_sequence/iterator_value_not_int.wren
+++ b/test/core/string_code_point_sequence/iterator_value_not_int.wren
@@ -1 +1 @@
-IO.print("string".codePoints.iteratorValue(12.34)) // expect runtime error: Index must be an integer.
+System.print("string".codePoints.iteratorValue(12.34)) // expect runtime error: Index must be an integer.
diff --git a/test/core/string_code_point_sequence/iterator_value_not_num.wren b/test/core/string_code_point_sequence/iterator_value_not_num.wren
index f0c9d4fb..8fcb3c16 100644
--- a/test/core/string_code_point_sequence/iterator_value_not_num.wren
+++ b/test/core/string_code_point_sequence/iterator_value_not_num.wren
@@ -1 +1 @@
-IO.print("string".codePoints.iteratorValue("not num")) // expect runtime error: Index must be a number.
+System.print("string".codePoints.iteratorValue("not num")) // expect runtime error: Index must be a number.
diff --git a/test/core/string_code_point_sequence/iterator_value_too_large.wren b/test/core/string_code_point_sequence/iterator_value_too_large.wren
index 8e8598c4..67c73703 100644
--- a/test/core/string_code_point_sequence/iterator_value_too_large.wren
+++ b/test/core/string_code_point_sequence/iterator_value_too_large.wren
@@ -1 +1 @@
-IO.print("string".codePoints.iteratorValue(6)) // expect runtime error: Index out of bounds.
+System.print("string".codePoints.iteratorValue(6)) // expect runtime error: Index out of bounds.
diff --git a/test/core/string_code_point_sequence/iterator_value_too_small.wren b/test/core/string_code_point_sequence/iterator_value_too_small.wren
index 2fd95fa9..07c9ebf8 100644
--- a/test/core/string_code_point_sequence/iterator_value_too_small.wren
+++ b/test/core/string_code_point_sequence/iterator_value_too_small.wren
@@ -1 +1 @@
-IO.print("string".codePoints.iteratorValue(-7)) // expect runtime error: Index out of bounds.
+System.print("string".codePoints.iteratorValue(-7)) // expect runtime error: Index out of bounds.
diff --git a/test/core/string_code_point_sequence/subscript.wren b/test/core/string_code_point_sequence/subscript.wren
index 3e250bcf..8db638df 100644
--- a/test/core/string_code_point_sequence/subscript.wren
+++ b/test/core/string_code_point_sequence/subscript.wren
@@ -3,40 +3,40 @@
 // Chars: sø mé ஃ  thî ng
 var codePoints = "søméஃthîng".codePoints
 
-IO.print(codePoints[0]) // expect: 115
-IO.print(codePoints[1]) // expect: 248
-IO.print(codePoints[2]) // expect: -1
-IO.print(codePoints[3]) // expect: 109
-IO.print(codePoints[4]) // expect: 233
-IO.print(codePoints[5]) // expect: -1
-IO.print(codePoints[6]) // expect: 2947
-IO.print(codePoints[7]) // expect: -1
-IO.print(codePoints[8]) // expect: -1
-IO.print(codePoints[9]) // expect: 116
-IO.print(codePoints[10]) // expect: 104
-IO.print(codePoints[11]) // expect: 238
-IO.print(codePoints[12]) // expect: -1
-IO.print(codePoints[13]) // expect: 110
-IO.print(codePoints[14]) // expect: 103
+System.print(codePoints[0]) // expect: 115
+System.print(codePoints[1]) // expect: 248
+System.print(codePoints[2]) // expect: -1
+System.print(codePoints[3]) // expect: 109
+System.print(codePoints[4]) // expect: 233
+System.print(codePoints[5]) // expect: -1
+System.print(codePoints[6]) // expect: 2947
+System.print(codePoints[7]) // expect: -1
+System.print(codePoints[8]) // expect: -1
+System.print(codePoints[9]) // expect: 116
+System.print(codePoints[10]) // expect: 104
+System.print(codePoints[11]) // expect: 238
+System.print(codePoints[12]) // expect: -1
+System.print(codePoints[13]) // expect: 110
+System.print(codePoints[14]) // expect: 103
 
-IO.print(codePoints[-15]) // expect: 115
-IO.print(codePoints[-14]) // expect: 248
-IO.print(codePoints[-13]) // expect: -1
-IO.print(codePoints[-12]) // expect: 109
-IO.print(codePoints[-11]) // expect: 233
-IO.print(codePoints[-10]) // expect: -1
-IO.print(codePoints[-9]) // expect: 2947
-IO.print(codePoints[-8]) // expect: -1
-IO.print(codePoints[-7]) // expect: -1
-IO.print(codePoints[-6]) // expect: 116
-IO.print(codePoints[-5]) // expect: 104
-IO.print(codePoints[-4]) // expect: 238
-IO.print(codePoints[-3]) // expect: -1
-IO.print(codePoints[-2]) // expect: 110
-IO.print(codePoints[-1]) // expect: 103
+System.print(codePoints[-15]) // expect: 115
+System.print(codePoints[-14]) // expect: 248
+System.print(codePoints[-13]) // expect: -1
+System.print(codePoints[-12]) // expect: 109
+System.print(codePoints[-11]) // expect: 233
+System.print(codePoints[-10]) // expect: -1
+System.print(codePoints[-9]) // expect: 2947
+System.print(codePoints[-8]) // expect: -1
+System.print(codePoints[-7]) // expect: -1
+System.print(codePoints[-6]) // expect: 116
+System.print(codePoints[-5]) // expect: 104
+System.print(codePoints[-4]) // expect: 238
+System.print(codePoints[-3]) // expect: -1
+System.print(codePoints[-2]) // expect: 110
+System.print(codePoints[-1]) // expect: 103
 
-IO.print("\0".codePoints[0]) // expect: 0
+System.print("\0".codePoints[0]) // expect: 0
 
 // Returns -1 for invalid UTF-8 sequences.
-IO.print("\xef\xf7".codePoints[0]) // expect: -1
-IO.print("\xef\xf7".codePoints[1]) // expect: -1
+System.print("\xef\xf7".codePoints[0]) // expect: -1
+System.print("\xef\xf7".codePoints[1]) // expect: -1
diff --git a/test/core/string_code_point_sequence/subscript_incomplete.wren b/test/core/string_code_point_sequence/subscript_incomplete.wren
index 2a280213..ca48400f 100644
--- a/test/core/string_code_point_sequence/subscript_incomplete.wren
+++ b/test/core/string_code_point_sequence/subscript_incomplete.wren
@@ -1,8 +1,8 @@
 // The first byte of a two-octet sequence.
-IO.print("\xc0".codePoints[0]) // expect: -1
+System.print("\xc0".codePoints[0]) // expect: -1
 
 // The first byte of a three-octet sequence.
-IO.print("\xe0".codePoints[0]) // expect: -1
+System.print("\xe0".codePoints[0]) // expect: -1
 
 // The first two bytes of a three-octet sequence.
-IO.print("\xe0\xae".codePoints[0]) // expect: -1
+System.print("\xe0\xae".codePoints[0]) // expect: -1
diff --git a/test/core/string_code_point_sequence/subscript_not_int.wren b/test/core/string_code_point_sequence/subscript_not_int.wren
index acc7d5bc..2ed30a1c 100644
--- a/test/core/string_code_point_sequence/subscript_not_int.wren
+++ b/test/core/string_code_point_sequence/subscript_not_int.wren
@@ -1 +1 @@
-IO.print("string".codePoints[12.34]) // expect runtime error: Index must be an integer.
+System.print("string".codePoints[12.34]) // expect runtime error: Index must be an integer.
diff --git a/test/core/string_code_point_sequence/subscript_not_num.wren b/test/core/string_code_point_sequence/subscript_not_num.wren
index 07dcf851..069686c4 100644
--- a/test/core/string_code_point_sequence/subscript_not_num.wren
+++ b/test/core/string_code_point_sequence/subscript_not_num.wren
@@ -1 +1 @@
-IO.print("string".codePoints["not num"]) // expect runtime error: Index must be a number.
+System.print("string".codePoints["not num"]) // expect runtime error: Index must be a number.
diff --git a/test/core/string_code_point_sequence/subscript_too_large.wren b/test/core/string_code_point_sequence/subscript_too_large.wren
index fb40d9d7..f5681d7c 100644
--- a/test/core/string_code_point_sequence/subscript_too_large.wren
+++ b/test/core/string_code_point_sequence/subscript_too_large.wren
@@ -1 +1 @@
-IO.print("string".codePoints[6]) // expect runtime error: Index out of bounds.
+System.print("string".codePoints[6]) // expect runtime error: Index out of bounds.
diff --git a/test/core/string_code_point_sequence/subscript_too_small.wren b/test/core/string_code_point_sequence/subscript_too_small.wren
index 5928ce7d..1cf42cd3 100644
--- a/test/core/string_code_point_sequence/subscript_too_small.wren
+++ b/test/core/string_code_point_sequence/subscript_too_small.wren
@@ -1 +1 @@
-IO.print("string".codePoints[-7]) // expect runtime error: Index out of bounds.
+System.print("string".codePoints[-7]) // expect runtime error: Index out of bounds.
diff --git a/test/core/system/print.wren b/test/core/system/print.wren
new file mode 100644
index 00000000..60d4df3c
--- /dev/null
+++ b/test/core/system/print.wren
@@ -0,0 +1,12 @@
+class Foo {
+  construct new() {}
+
+  toString { "Foo.toString" }
+}
+
+// Calls toString on argument.
+System.print(Foo.new()) // expect: Foo.toString
+
+// Returns the argument.
+System.print(System.print(1) == 1) // expect: 1
+                                   // expect: true
diff --git a/test/core/system/print_all.wren b/test/core/system/print_all.wren
new file mode 100644
index 00000000..202524bd
--- /dev/null
+++ b/test/core/system/print_all.wren
@@ -0,0 +1,8 @@
+class Foo {
+  construct new() {}
+
+  toString { "Foo" }
+}
+
+System.printAll([]) // expect:
+System.printAll([1, true, Foo.new(), "s"]) // expect: 1trueFoos
diff --git a/test/core/system/print_all_not_sequence.wren b/test/core/system/print_all_not_sequence.wren
new file mode 100644
index 00000000..f47831aa
--- /dev/null
+++ b/test/core/system/print_all_not_sequence.wren
@@ -0,0 +1 @@
+System.printAll(123) // expect runtime error: Num does not implement 'iterate(_)'.
diff --git a/test/core/system/print_bad_to_string.wren b/test/core/system/print_bad_to_string.wren
new file mode 100644
index 00000000..fdae6e71
--- /dev/null
+++ b/test/core/system/print_bad_to_string.wren
@@ -0,0 +1,6 @@
+class BadToString {
+  construct new() {}
+  toString { 3 }
+}
+
+System.print(BadToString.new()) // expect: [invalid toString]
diff --git a/test/core/system/write_all.wren b/test/core/system/write_all.wren
new file mode 100644
index 00000000..8bca90dd
--- /dev/null
+++ b/test/core/system/write_all.wren
@@ -0,0 +1,10 @@
+class Foo {
+  construct new() {}
+
+  toString { "Foo" }
+}
+
+System.writeAll([]) // expect:
+System.print()
+System.writeAll([1, true, Foo.new(), "s"]) // expect: 1trueFoos
+System.print()
diff --git a/test/core/system/write_all_not_sequence.wren b/test/core/system/write_all_not_sequence.wren
new file mode 100644
index 00000000..3d158977
--- /dev/null
+++ b/test/core/system/write_all_not_sequence.wren
@@ -0,0 +1 @@
+System.writeAll(123) // expect runtime error: Num does not implement 'iterate(_)'.
diff --git a/test/core/system/write_bad_to_string.wren b/test/core/system/write_bad_to_string.wren
new file mode 100644
index 00000000..bb0a1a1b
--- /dev/null
+++ b/test/core/system/write_bad_to_string.wren
@@ -0,0 +1,7 @@
+class BadToString {
+  construct new() {}
+  toString { 3 }
+}
+
+System.write(BadToString.new())
+System.print("!") // expect: [invalid toString]!
diff --git a/test/io/print.wren b/test/io/print.wren
deleted file mode 100644
index c02647d8..00000000
--- a/test/io/print.wren
+++ /dev/null
@@ -1,34 +0,0 @@
-class Foo {
-  construct new() {}
-
-  toString { "Foo.toString" }
-}
-
-// Calls toString on argument.
-IO.print(Foo.new()) // expect: Foo.toString
-
-// With one argument, returns the argument.
-IO.print(IO.print(1) == 1) // expect: 1
-                           // expect: true
-
-// With more than one argument, returns null.
-IO.print(IO.print(1, 2) == null) // expect: 12
-                                 // expect: true
-
-// Allows multiple arguments and concatenates them.
-IO.print(1) // expect: 1
-IO.print(1, 2) // expect: 12
-IO.print(1, 2, 3) // expect: 123
-IO.print(1, 2, 3, 4) // expect: 1234
-IO.print(1, 2, 3, 4, 5) // expect: 12345
-IO.print(1, 2, 3, 4, 5, 6) // expect: 123456
-IO.print(1, 2, 3, 4, 5, 6, 7) // expect: 1234567
-IO.print(1, 2, 3, 4, 5, 6, 7, 8) // expect: 12345678
-IO.print(1, 2, 3, 4, 5, 6, 7, 8, 9) // expect: 123456789
-IO.print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10) // expect: 12345678910
-IO.print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11) // expect: 1234567891011
-IO.print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) // expect: 123456789101112
-IO.print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13) // expect: 12345678910111213
-IO.print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14) // expect: 1234567891011121314
-IO.print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15) // expect: 123456789101112131415
-IO.print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16) // expect: 12345678910111213141516
diff --git a/test/io/print_bad_to_string.wren b/test/io/print_bad_to_string.wren
deleted file mode 100644
index af750175..00000000
--- a/test/io/print_bad_to_string.wren
+++ /dev/null
@@ -1,6 +0,0 @@
-class BadToString {
-  construct new() {}
-  toString { 3 }
-}
-
-IO.print(BadToString.new()) // expect: [invalid toString]
diff --git a/test/io/read.wren b/test/io/read.wren
deleted file mode 100644
index 0b542f6e..00000000
--- a/test/io/read.wren
+++ /dev/null
@@ -1,13 +0,0 @@
-var a = IO.read("a:") // stdin: first
-var b = IO.read("b:") // stdin: second
-IO.print
-// Using write() here because the read lines include the trailing newline.
-IO.write(a)
-IO.write(b)
-
-// Since stdin isn't echoed back to stdout, we don't see the input lines here,
-// and there is no newline between the two prompts since that normally comes
-// from the input itself.
-// expect: a:b:
-// expect: first
-// expect: second
\ No newline at end of file
diff --git a/test/io/read_arg_not_string.wren b/test/io/read_arg_not_string.wren
deleted file mode 100644
index 85a23892..00000000
--- a/test/io/read_arg_not_string.wren
+++ /dev/null
@@ -1 +0,0 @@
-IO.read(null) // expect runtime error: Prompt must be a string.
diff --git a/test/io/read_eof.wren b/test/io/read_eof.wren
deleted file mode 100644
index db9045aa..00000000
--- a/test/io/read_eof.wren
+++ /dev/null
@@ -1 +0,0 @@
-IO.write(IO.read()) // expect: null
diff --git a/test/io/write_bad_to_string.wren b/test/io/write_bad_to_string.wren
deleted file mode 100644
index df9d3b66..00000000
--- a/test/io/write_bad_to_string.wren
+++ /dev/null
@@ -1,7 +0,0 @@
-class BadToString {
-  construct new() {}
-  toString { 3 }
-}
-
-IO.write(BadToString.new()) // expect: [invalid toString]
-IO.print
\ No newline at end of file
diff --git a/test/language/assignment/associativity.wren b/test/language/assignment/associativity.wren
index e7844499..40967585 100644
--- a/test/language/assignment/associativity.wren
+++ b/test/language/assignment/associativity.wren
@@ -4,6 +4,6 @@ var c = "c"
 
 // Assignment is right-associative.
 a = b = c
-IO.print(a) // expect: c
-IO.print(b) // expect: c
-IO.print(c) // expect: c
+System.print(a) // expect: c
+System.print(b) // expect: c
+System.print(c) // expect: c
diff --git a/test/language/assignment/global.wren b/test/language/assignment/global.wren
index fa070409..07123462 100644
--- a/test/language/assignment/global.wren
+++ b/test/language/assignment/global.wren
@@ -1,8 +1,8 @@
 var a = "before"
-IO.print(a) // expect: before
+System.print(a) // expect: before
 
 a = "after"
-IO.print(a) // expect: after
+System.print(a) // expect: after
 
-IO.print(a = "arg") // expect: arg
-IO.print(a) // expect: arg
+System.print(a = "arg") // expect: arg
+System.print(a) // expect: arg
diff --git a/test/language/assignment/local.wren b/test/language/assignment/local.wren
index 3805a7bd..926d31c2 100644
--- a/test/language/assignment/local.wren
+++ b/test/language/assignment/local.wren
@@ -1,10 +1,10 @@
 Fn.new {
   var a = "before"
-  IO.print(a) // expect: before
+  System.print(a) // expect: before
 
   a = "after"
-  IO.print(a) // expect: after
+  System.print(a) // expect: after
 
-  IO.print(a = "arg") // expect: arg
-  IO.print(a) // expect: arg
+  System.print(a = "arg") // expect: arg
+  System.print(a) // expect: arg
 }.call()
diff --git a/test/language/assignment/syntax.wren b/test/language/assignment/syntax.wren
index f283a5bd..7cf97b47 100644
--- a/test/language/assignment/syntax.wren
+++ b/test/language/assignment/syntax.wren
@@ -2,10 +2,10 @@
 var a = "a"
 var b = "b"
 a = b = "chain"
-IO.print(a) // expect: chain
-IO.print(a) // expect: chain
+System.print(a) // expect: chain
+System.print(a) // expect: chain
 
 // Assignment on RHS of variable.
 var c = a = "var"
-IO.print(a) // expect: var
-IO.print(c) // expect: var
+System.print(a) // expect: var
+System.print(c) // expect: var
diff --git a/test/language/bitwise_precedence.wren b/test/language/bitwise_precedence.wren
index 91651136..d685e26d 100644
--- a/test/language/bitwise_precedence.wren
+++ b/test/language/bitwise_precedence.wren
@@ -1,23 +1,23 @@
 // << have higher precedence than |.
-IO.print(2 | 1 << 1) // expect: 2
-IO.print(1 << 1 | 2) // expect: 2
+System.print(2 | 1 << 1) // expect: 2
+System.print(1 << 1 | 2) // expect: 2
 
 // << has higher precedence than &.
-IO.print(2 & 1 << 1) // expect: 2
-IO.print(1 << 1 & 2) // expect: 2
+System.print(2 & 1 << 1) // expect: 2
+System.print(1 << 1 & 2) // expect: 2
 
 // << has higher precedence than ^.
-IO.print(2 ^ 1 << 1) // expect: 0
-IO.print(1 << 1 ^ 2) // expect: 0
+System.print(2 ^ 1 << 1) // expect: 0
+System.print(1 << 1 ^ 2) // expect: 0
 
 // & has higher precedence than |.
-IO.print(1 & 1 | 2) // expect: 3
-IO.print(2 | 1 & 1) // expect: 3
+System.print(1 & 1 | 2) // expect: 3
+System.print(2 | 1 & 1) // expect: 3
 
 // & has higher precedence than ^.
-IO.print(1 & 1 ^ 2) // expect: 3
-IO.print(2 ^ 1 & 1) // expect: 3
+System.print(1 & 1 ^ 2) // expect: 3
+System.print(2 ^ 1 & 1) // expect: 3
 
 // ^ has higher precedence than |.
-IO.print(1 ^ 1 | 1) // expect: 1
-IO.print(1 | 1 ^ 1) // expect: 1
+System.print(1 ^ 1 | 1) // expect: 1
+System.print(1 | 1 ^ 1) // expect: 1
diff --git a/test/language/break/closure_in_for.wren b/test/language/break/closure_in_for.wren
index 2c204f50..1d41b116 100644
--- a/test/language/break/closure_in_for.wren
+++ b/test/language/break/closure_in_for.wren
@@ -1,7 +1,7 @@
 var f
 for (i in [1, 2, 3]) {
   var j = 4
-  f = Fn.new { IO.print(i + j) }
+  f = Fn.new { System.print(i + j) }
   break
 }
 
diff --git a/test/language/break/closure_in_while.wren b/test/language/break/closure_in_while.wren
index 084b6c46..38457650 100644
--- a/test/language/break/closure_in_while.wren
+++ b/test/language/break/closure_in_while.wren
@@ -1,7 +1,7 @@
 var f
 while (true) {
   var i = "i"
-  f = Fn.new { IO.print(i) }
+  f = Fn.new { System.print(i) }
   break
 }
 
diff --git a/test/language/break/exit_local_scopes.wren b/test/language/break/exit_local_scopes.wren
index fdf8344f..242f3ecb 100644
--- a/test/language/break/exit_local_scopes.wren
+++ b/test/language/break/exit_local_scopes.wren
@@ -1,5 +1,5 @@
 for (i in 0..10) {
-  IO.print(i)
+  System.print(i)
 
   {
     var a = "a"
diff --git a/test/language/break/in_for_loop.wren b/test/language/break/in_for_loop.wren
index 67479f33..78dbb0ab 100644
--- a/test/language/break/in_for_loop.wren
+++ b/test/language/break/in_for_loop.wren
@@ -1,7 +1,7 @@
 for (i in [1, 2, 3, 4, 5]) {
-  IO.print(i)
+  System.print(i)
   if (i > 2) break
-  IO.print(i)
+  System.print(i)
 }
 // expect: 1
 // expect: 1
diff --git a/test/language/break/in_while_loop.wren b/test/language/break/in_while_loop.wren
index 9ef4fb5f..bdc96fc4 100644
--- a/test/language/break/in_while_loop.wren
+++ b/test/language/break/in_while_loop.wren
@@ -1,9 +1,9 @@
 var i = 0
 while (true) {
   i = i + 1
-  IO.print(i)
+  System.print(i)
   if (i > 2) break
-  IO.print(i)
+  System.print(i)
 }
 // expect: 1
 // expect: 1
diff --git a/test/language/break/nested_for_loop.wren b/test/language/break/nested_for_loop.wren
index 514aa620..167a4e91 100644
--- a/test/language/break/nested_for_loop.wren
+++ b/test/language/break/nested_for_loop.wren
@@ -1,9 +1,9 @@
 for (i in 0..2) {
-  IO.print("outer ", i)
+  System.print("outer " + i.toString)
   if (i > 1) break
 
   for (j in 0..2) {
-    IO.print("inner ", j)
+    System.print("inner " + j.toString)
     if (j > 1) break
   }
 }
diff --git a/test/language/break/nested_while_loop.wren b/test/language/break/nested_while_loop.wren
index 7186cd7d..8146613c 100644
--- a/test/language/break/nested_while_loop.wren
+++ b/test/language/break/nested_while_loop.wren
@@ -1,11 +1,11 @@
 var i = 0
 while (true) {
-  IO.print("outer ", i)
+  System.print("outer " + i.toString)
   if (i > 1) break
 
   var j = 0
   while (true) {
-    IO.print("inner ", j)
+    System.print("inner " + j.toString)
     if (j > 1) break
 
     j = j + 1
diff --git a/test/language/class/field_in_foreign_class.wren b/test/language/class/field_in_foreign_class.wren
index 5b7c2c26..4049b746 100644
--- a/test/language/class/field_in_foreign_class.wren
+++ b/test/language/class/field_in_foreign_class.wren
@@ -1,7 +1,7 @@
 foreign class Foo {
   bar {
     // Can't read a field.
-    IO.print(_bar) // expect error
+    System.print(_bar) // expect error
 
     // Or write one.
     _bar = "value" // expect error
diff --git a/test/language/class/lowercase_name_inside_body.wren b/test/language/class/lowercase_name_inside_body.wren
index 6819fd70..c2eac488 100644
--- a/test/language/class/lowercase_name_inside_body.wren
+++ b/test/language/class/lowercase_name_inside_body.wren
@@ -2,11 +2,11 @@ class foo {
   construct new() {}
 
   static callFoo {
-    IO.print(foo)
+    System.print(foo)
   }
 
   callFoo {
-    IO.print(foo)
+    System.print(foo)
   }
 
   foo { "instance foo method" }
diff --git a/test/language/class/name_inside_body.wren b/test/language/class/name_inside_body.wren
index 477777c0..eb1fa838 100644
--- a/test/language/class/name_inside_body.wren
+++ b/test/language/class/name_inside_body.wren
@@ -2,11 +2,11 @@ class Foo {
   construct new() {}
 
   static sayName {
-    IO.print(Foo)
+    System.print(Foo)
   }
 
   sayName {
-    IO.print(Foo)
+    System.print(Foo)
   }
 
   static toString { "Foo!" }
diff --git a/test/language/closure/assign_to_closure.wren b/test/language/closure/assign_to_closure.wren
index 37a76fce..9de47de5 100644
--- a/test/language/closure/assign_to_closure.wren
+++ b/test/language/closure/assign_to_closure.wren
@@ -4,15 +4,15 @@ var g = null
 {
   var local = "local"
   f = Fn.new {
-    IO.print(local)
+    System.print(local)
     local = "after f"
-    IO.print(local)
+    System.print(local)
   }
 
   g = Fn.new {
-    IO.print(local)
+    System.print(local)
     local = "after g"
-    IO.print(local)
+    System.print(local)
   }
 }
 
diff --git a/test/language/closure/close_over_function_parameter.wren b/test/language/closure/close_over_function_parameter.wren
index 9a786ff3..f5deaca3 100644
--- a/test/language/closure/close_over_function_parameter.wren
+++ b/test/language/closure/close_over_function_parameter.wren
@@ -2,7 +2,7 @@ var f = null
 
 Fn.new {|param|
   f = Fn.new {
-    IO.print(param)
+    System.print(param)
   }
 }.call("param")
 
diff --git a/test/language/closure/close_over_later_variable.wren b/test/language/closure/close_over_later_variable.wren
index 719b9d75..d948c7da 100644
--- a/test/language/closure/close_over_later_variable.wren
+++ b/test/language/closure/close_over_later_variable.wren
@@ -7,7 +7,7 @@ Fn.new {
   var a = "a"
   var b = "b"
   Fn.new {
-    IO.print(b) // expect: b
-    IO.print(a) // expect: a
+    System.print(b) // expect: b
+    System.print(a) // expect: a
   }.call()
 }.call()
diff --git a/test/language/closure/close_over_method_parameter.wren b/test/language/closure/close_over_method_parameter.wren
index f1aa8080..9b309f58 100644
--- a/test/language/closure/close_over_method_parameter.wren
+++ b/test/language/closure/close_over_method_parameter.wren
@@ -5,7 +5,7 @@ class Foo {
 
   method(param) {
     F = Fn.new {
-      IO.print(param)
+      System.print(param)
     }
   }
 }
diff --git a/test/language/closure/closed_closure_in_function.wren b/test/language/closure/closed_closure_in_function.wren
index d3e8d6c5..ea3aba50 100644
--- a/test/language/closure/closed_closure_in_function.wren
+++ b/test/language/closure/closed_closure_in_function.wren
@@ -3,7 +3,7 @@ var f = null
 {
   var local = "local"
   f = Fn.new {
-    IO.print(local)
+    System.print(local)
   }
 }
 
diff --git a/test/language/closure/closed_closure_in_method.wren b/test/language/closure/closed_closure_in_method.wren
index 44971792..027e27aa 100644
--- a/test/language/closure/closed_closure_in_method.wren
+++ b/test/language/closure/closed_closure_in_method.wren
@@ -7,7 +7,7 @@ var foo = null
     construct new() {}
 
     method {
-      IO.print(local)
+      System.print(local)
     }
   }
 
diff --git a/test/language/closure/nested_closure.wren b/test/language/closure/nested_closure.wren
index b4e239d5..234a3ae2 100644
--- a/test/language/closure/nested_closure.wren
+++ b/test/language/closure/nested_closure.wren
@@ -7,9 +7,9 @@ Fn.new {
     Fn.new {
       var c = "c"
       f = Fn.new {
-        IO.print(a)
-        IO.print(b)
-        IO.print(c)
+        System.print(a)
+        System.print(b)
+        System.print(c)
       }
     }.call()
   }.call()
diff --git a/test/language/closure/open_closure_in_function.wren b/test/language/closure/open_closure_in_function.wren
index a49585e2..34dbd58e 100644
--- a/test/language/closure/open_closure_in_function.wren
+++ b/test/language/closure/open_closure_in_function.wren
@@ -1,6 +1,6 @@
 {
   var local = "local"
   Fn.new {
-    IO.print(local) // expect: local
+    System.print(local) // expect: local
   }.call()
 }
diff --git a/test/language/closure/open_closure_in_method.wren b/test/language/closure/open_closure_in_method.wren
index 977dbe59..32abd318 100644
--- a/test/language/closure/open_closure_in_method.wren
+++ b/test/language/closure/open_closure_in_method.wren
@@ -5,7 +5,7 @@
     construct new() {}
 
     method {
-      IO.print(local)
+      System.print(local)
     }
   }
 
diff --git a/test/language/closure/reference_closure_multiple_times.wren b/test/language/closure/reference_closure_multiple_times.wren
index 0d9f79cd..98b8ea38 100644
--- a/test/language/closure/reference_closure_multiple_times.wren
+++ b/test/language/closure/reference_closure_multiple_times.wren
@@ -3,8 +3,8 @@ var f = null
 {
   var a = "a"
   f = Fn.new {
-    IO.print(a)
-    IO.print(a)
+    System.print(a)
+    System.print(a)
   }
 }
 
diff --git a/test/language/closure/reuse_closure_slot.wren b/test/language/closure/reuse_closure_slot.wren
index f9de1a4f..0125fc07 100644
--- a/test/language/closure/reuse_closure_slot.wren
+++ b/test/language/closure/reuse_closure_slot.wren
@@ -3,7 +3,7 @@
 
   {
     var a = "a"
-    f = Fn.new { IO.print(a) }
+    f = Fn.new { System.print(a) }
   }
 
   {
diff --git a/test/language/closure/shadow_closure_with_local.wren b/test/language/closure/shadow_closure_with_local.wren
index 34f29986..c7de20e8 100644
--- a/test/language/closure/shadow_closure_with_local.wren
+++ b/test/language/closure/shadow_closure_with_local.wren
@@ -2,10 +2,10 @@
   var foo = "closure"
   Fn.new {
     {
-      IO.print(foo) // expect: closure
+      System.print(foo) // expect: closure
       var foo = "shadow"
-      IO.print(foo) // expect: shadow
+      System.print(foo) // expect: shadow
     }
-    IO.print(foo) // expect: closure
+    System.print(foo) // expect: closure
   }.call()
 }
diff --git a/test/language/comments/block.wren b/test/language/comments/block.wren
index bf7d5b81..956d6832 100644
--- a/test/language/comments/block.wren
+++ b/test/language/comments/block.wren
@@ -1,5 +1,5 @@
 // In middle of line.
-IO.print/* ... */(/* */"ok"/* */) // expect: ok
+System.print/* ... */(/* */"ok"/* */) // expect: ok
 
 // Nested.
-IO.print(/* in /* nest */ out */"ok") // expect: ok
+System.print(/* in /* nest */ out */"ok") // expect: ok
diff --git a/test/language/comments/block_at_eof.wren b/test/language/comments/block_at_eof.wren
index a7e1bf7a..57bbca27 100644
--- a/test/language/comments/block_at_eof.wren
+++ b/test/language/comments/block_at_eof.wren
@@ -1,2 +1,2 @@
-IO.print("ok") // expect: ok
+System.print("ok") // expect: ok
 /* comment */
\ No newline at end of file
diff --git a/test/language/comments/line_at_eof.wren b/test/language/comments/line_at_eof.wren
index f450eab8..8df57dc0 100644
--- a/test/language/comments/line_at_eof.wren
+++ b/test/language/comments/line_at_eof.wren
@@ -1,2 +1,2 @@
-IO.print("ok") // expect: ok
+System.print("ok") // expect: ok
 // comment
\ No newline at end of file
diff --git a/test/language/comments/unicode.wren b/test/language/comments/unicode.wren
index 06e65898..c3ebc155 100644
--- a/test/language/comments/unicode.wren
+++ b/test/language/comments/unicode.wren
@@ -8,4 +8,4 @@
 
 // TODO: What about combining characters?
 
-IO.print("ok") // expect: ok
+System.print("ok") // expect: ok
diff --git a/test/language/comments/unterminated_block.wren b/test/language/comments/unterminated_block.wren
index 1c39563d..6878f959 100644
--- a/test/language/comments/unterminated_block.wren
+++ b/test/language/comments/unterminated_block.wren
@@ -1,3 +1,3 @@
 // expect error line 3
-IO.print("nope") /*
+System.print("nope") /*
 oops
\ No newline at end of file
diff --git a/test/language/comments/unterminated_nested_block.wren b/test/language/comments/unterminated_nested_block.wren
index 0afe4ff1..001df6f9 100644
--- a/test/language/comments/unterminated_nested_block.wren
+++ b/test/language/comments/unterminated_nested_block.wren
@@ -1,4 +1,4 @@
 // expect error line 4
-IO.print("nope") /* /* /*
+System.print("nope") /* /* /*
 */
 oops
\ No newline at end of file
diff --git a/test/language/conditional/newlines.wren b/test/language/conditional/newlines.wren
index a253b0c5..ae99fc0e 100644
--- a/test/language/conditional/newlines.wren
+++ b/test/language/conditional/newlines.wren
@@ -1,7 +1,7 @@
 // Newline after '?'.
-IO.print(true ?
+System.print(true ?
   "yes" : "no") // expect: yes
 
 // Newline after ':'.
-IO.print(false ? "yes" :
+System.print(false ? "yes" :
   "no") // expect: no
diff --git a/test/language/conditional/precedence.wren b/test/language/conditional/precedence.wren
index d24a7fef..ddd08e9c 100644
--- a/test/language/conditional/precedence.wren
+++ b/test/language/conditional/precedence.wren
@@ -5,52 +5,52 @@ class Foo {
 }
 
 // Condition precedence.
-IO.print(true ? 1 : 2) // expect: 1
-IO.print((true) ? 1 : 2) // expect: 1
-IO.print([true][0] ? 1 : 2) // expect: 1
-IO.print(Foo.bar ? 1 : 2) // expect: 1
-IO.print(3..4 ? 1 : 2) // expect: 1
-IO.print(3 * 4 ? 1 : 2) // expect: 1
-IO.print(3 + 4 ? 1 : 2) // expect: 1
-IO.print(true || false ? 1 : 2) // expect: 1
-IO.print(!false ? 1 : 2) // expect: 1
-IO.print(~0 ? 1 : 2) // expect: 1
-IO.print(3 is Num ? 1 : 2) // expect: 1
-IO.print(Foo.new() ? 1 : 2) // expect: 1
+System.print(true ? 1 : 2) // expect: 1
+System.print((true) ? 1 : 2) // expect: 1
+System.print([true][0] ? 1 : 2) // expect: 1
+System.print(Foo.bar ? 1 : 2) // expect: 1
+System.print(3..4 ? 1 : 2) // expect: 1
+System.print(3 * 4 ? 1 : 2) // expect: 1
+System.print(3 + 4 ? 1 : 2) // expect: 1
+System.print(true || false ? 1 : 2) // expect: 1
+System.print(!false ? 1 : 2) // expect: 1
+System.print(~0 ? 1 : 2) // expect: 1
+System.print(3 is Num ? 1 : 2) // expect: 1
+System.print(Foo.new() ? 1 : 2) // expect: 1
 
 var a = 0
-IO.print(a = 3 ? 1 : 2) // expect: 1
-IO.print(a) // expect: 1
+System.print(a = 3 ? 1 : 2) // expect: 1
+System.print(a) // expect: 1
 
 // Then branch precedence.
-IO.print(true ? (1) : 2) // expect: 1
-IO.print(true ? [1][0] : 2) // expect: 1
-IO.print(true ? Foo.baz : 2) // expect: 1
-IO.print(true ? 3..4 : 2) // expect: 3..4
-IO.print(true ? 3 * 4 : 2) // expect: 12
-IO.print(true ? 3 + 4 : 2) // expect: 7
-IO.print(true ? 1 || false : 2) // expect: 1
-IO.print(true ? !true : 2) // expect: false
-IO.print(true ? ~0 : 2) // expect: 4294967295
-IO.print(true ? 3 is Bool : 2) // expect: false
-IO.print(true ? Foo.new() : 2) // expect: instance of Foo
+System.print(true ? (1) : 2) // expect: 1
+System.print(true ? [1][0] : 2) // expect: 1
+System.print(true ? Foo.baz : 2) // expect: 1
+System.print(true ? 3..4 : 2) // expect: 3..4
+System.print(true ? 3 * 4 : 2) // expect: 12
+System.print(true ? 3 + 4 : 2) // expect: 7
+System.print(true ? 1 || false : 2) // expect: 1
+System.print(true ? !true : 2) // expect: false
+System.print(true ? ~0 : 2) // expect: 4294967295
+System.print(true ? 3 is Bool : 2) // expect: false
+System.print(true ? Foo.new() : 2) // expect: instance of Foo
 
-IO.print(true ? a = 5 : 2) // expect: 5
-IO.print(a) // expect: 5
+System.print(true ? a = 5 : 2) // expect: 5
+System.print(a) // expect: 5
 
 // Else branch precedence.
-IO.print(false ? 1 : (2)) // expect: 2
-IO.print(false ? 1 : [2][0]) // expect: 2
-IO.print(false ? 2 : Foo.baz) // expect: 1
-IO.print(false ? 1 : 3..4) // expect: 3..4
-IO.print(false ? 1 : 3 * 4) // expect: 12
-IO.print(false ? 1 : 3 + 4) // expect: 7
-IO.print(false ? 1 : 2 || false) // expect: 2
-IO.print(false ? 1 : !false) // expect: true
-IO.print(false ? 1 : ~0) // expect: 4294967295
-IO.print(false ? 1 : 3 is Num) // expect: true
-IO.print(false ? 1 : Foo.new()) // expect: instance of Foo
+System.print(false ? 1 : (2)) // expect: 2
+System.print(false ? 1 : [2][0]) // expect: 2
+System.print(false ? 2 : Foo.baz) // expect: 1
+System.print(false ? 1 : 3..4) // expect: 3..4
+System.print(false ? 1 : 3 * 4) // expect: 12
+System.print(false ? 1 : 3 + 4) // expect: 7
+System.print(false ? 1 : 2 || false) // expect: 2
+System.print(false ? 1 : !false) // expect: true
+System.print(false ? 1 : ~0) // expect: 4294967295
+System.print(false ? 1 : 3 is Num) // expect: true
+System.print(false ? 1 : Foo.new()) // expect: instance of Foo
 
 // Associativity.
-IO.print(true ? 2 : true ? 4 : 5) // expect: 2
-IO.print(false ? 2 : true ? 4 : 5) // expect: 4
+System.print(true ? 2 : true ? 4 : 5) // expect: 2
+System.print(false ? 2 : true ? 4 : 5) // expect: 4
diff --git a/test/language/conditional/short_circuit.wren b/test/language/conditional/short_circuit.wren
index 21f37521..5dde752f 100644
--- a/test/language/conditional/short_circuit.wren
+++ b/test/language/conditional/short_circuit.wren
@@ -1,2 +1,2 @@
-true ? IO.print("ok") : IO.print("no") // expect: ok
-false ? IO.print("no") : IO.print("ok") // expect: ok
+true ? System.print("ok") : System.print("no") // expect: ok
+false ? System.print("no") : System.print("ok") // expect: ok
diff --git a/test/language/constructor/cannot_be_infix.wren b/test/language/constructor/cannot_be_infix.wren
index d5950e67..aa42484b 100644
--- a/test/language/constructor/cannot_be_infix.wren
+++ b/test/language/constructor/cannot_be_infix.wren
@@ -1,5 +1,5 @@
 class Foo {
   this +(value) { // expect error
-    IO.print("ok")
+    System.print("ok")
   }
 }
diff --git a/test/language/constructor/cannot_be_minus.wren b/test/language/constructor/cannot_be_minus.wren
index 75fbe5e9..934a1e4b 100644
--- a/test/language/constructor/cannot_be_minus.wren
+++ b/test/language/constructor/cannot_be_minus.wren
@@ -1,5 +1,5 @@
 class Foo {
   this -(value) { // expect error
-    IO.print("ok")
+    System.print("ok")
   }
 }
diff --git a/test/language/constructor/cannot_be_setter.wren b/test/language/constructor/cannot_be_setter.wren
index 773e34ff..a02092ec 100644
--- a/test/language/constructor/cannot_be_setter.wren
+++ b/test/language/constructor/cannot_be_setter.wren
@@ -1,5 +1,5 @@
 class Foo {
   this name=(value) { // expect error
-    IO.print("ok")
+    System.print("ok")
   }
 }
diff --git a/test/language/constructor/cannot_be_subscript.wren b/test/language/constructor/cannot_be_subscript.wren
index db798d1d..b3e09401 100644
--- a/test/language/constructor/cannot_be_subscript.wren
+++ b/test/language/constructor/cannot_be_subscript.wren
@@ -1,5 +1,5 @@
 class Foo {
   this [value] { // expect error
-    IO.print("ok")
+    System.print("ok")
   }
 }
diff --git a/test/language/constructor/cannot_be_unary.wren b/test/language/constructor/cannot_be_unary.wren
index ae15e9e3..fa7c7a26 100644
--- a/test/language/constructor/cannot_be_unary.wren
+++ b/test/language/constructor/cannot_be_unary.wren
@@ -1,5 +1,5 @@
 class Foo {
   this ! { // expect error
-    IO.print("ok")
+    System.print("ok")
   }
 }
diff --git a/test/language/constructor/cannot_call_initializer.wren b/test/language/constructor/cannot_call_initializer.wren
index 56a2993d..06e7e3cc 100644
--- a/test/language/constructor/cannot_call_initializer.wren
+++ b/test/language/constructor/cannot_call_initializer.wren
@@ -1,6 +1,6 @@
 class Foo {
   construct new() {
-    IO.print("ok")
+    System.print("ok")
   }
 }
 
diff --git a/test/language/constructor/named.wren b/test/language/constructor/named.wren
index b1fc23a1..2a0f2c50 100644
--- a/test/language/constructor/named.wren
+++ b/test/language/constructor/named.wren
@@ -5,10 +5,10 @@ class Foo {
   toString { _field }
 }
 
-IO.print(Foo.named()) // expect: named
-IO.print(Foo.other()) // expect: other
+System.print(Foo.named()) // expect: named
+System.print(Foo.other()) // expect: other
 
 // Returns the new instance.
 var foo = Foo.named()
-IO.print(foo is Foo) // expect: true
-IO.print(foo.toString) // expect: named
+System.print(foo is Foo) // expect: true
+System.print(foo.toString) // expect: named
diff --git a/test/language/constructor/no_parameter_list.wren b/test/language/constructor/no_parameter_list.wren
index 6de9df1b..5c0e232a 100644
--- a/test/language/constructor/no_parameter_list.wren
+++ b/test/language/constructor/no_parameter_list.wren
@@ -1,5 +1,5 @@
 class Foo {
   this new { // expect error
-    IO.print("ok")
+    System.print("ok")
   }
 }
diff --git a/test/language/constructor/superclass.wren b/test/language/constructor/superclass.wren
index e292c513..f645f39e 100644
--- a/test/language/constructor/superclass.wren
+++ b/test/language/constructor/superclass.wren
@@ -1,6 +1,6 @@
 class A {
   construct new(arg) {
-    IO.print("new A ", arg)
+    System.print("new A " + arg)
     _field = arg
   }
 
@@ -10,7 +10,7 @@ class A {
 class B is A {
   construct new(arg1, arg2) {
     super(arg2)
-    IO.print("new B ", arg1)
+    System.print("new B " + arg1)
     _field = arg1
   }
 
@@ -20,7 +20,7 @@ class B is A {
 class C is B {
   construct new() {
     super("one", "two")
-    IO.print("new C")
+    System.print("new C")
     _field = "c"
   }
 
@@ -31,10 +31,10 @@ var c = C.new()
 // expect: new A two
 // expect: new B one
 // expect: new C
-IO.print(c is A) // expect: true
-IO.print(c is B) // expect: true
-IO.print(c is C) // expect: true
+System.print(c is A) // expect: true
+System.print(c is B) // expect: true
+System.print(c is C) // expect: true
 
-IO.print(c.aField) // expect: two
-IO.print(c.bField) // expect: one
-IO.print(c.cField) // expect: c
+System.print(c.aField) // expect: two
+System.print(c.bField) // expect: one
+System.print(c.cField) // expect: c
diff --git a/test/language/empty_block.wren b/test/language/empty_block.wren
index cfe778ac..26f6fb43 100644
--- a/test/language/empty_block.wren
+++ b/test/language/empty_block.wren
@@ -4,4 +4,4 @@
 if (true) {}
 if (false) {} else {}
 
-IO.print("ok") // expect: ok
\ No newline at end of file
+System.print("ok") // expect: ok
\ No newline at end of file
diff --git a/test/language/fiber/closure.wren b/test/language/fiber/closure.wren
index 8a720dd7..5bf8db66 100644
--- a/test/language/fiber/closure.wren
+++ b/test/language/fiber/closure.wren
@@ -4,16 +4,16 @@ var closure
 {
   var a = "before"
   fiber = Fiber.new {
-    IO.print(a)
+    System.print(a)
     Fiber.yield()
     a = "after"
     Fiber.yield()
-    IO.print(a)
+    System.print(a)
     a = "final"
   }
 
   closure = Fn.new {
-    IO.print(a)
+    System.print(a)
   }
 }
 
diff --git a/test/language/field/closure.wren b/test/language/field/closure.wren
index 3f0c27ba..f8f34281 100644
--- a/test/language/field/closure.wren
+++ b/test/language/field/closure.wren
@@ -11,6 +11,6 @@ class Foo {
 }
 
 var foo = Foo.new()
-IO.print(foo.closeOverGet.call()) // expect: Foo field
+System.print(foo.closeOverGet.call()) // expect: Foo field
 foo.closeOverSet.call()
-IO.print(foo.closeOverGet.call()) // expect: new value
+System.print(foo.closeOverGet.call()) // expect: new value
diff --git a/test/language/field/default_to_null.wren b/test/language/field/default_to_null.wren
index 5b834f71..9cc0df1e 100644
--- a/test/language/field/default_to_null.wren
+++ b/test/language/field/default_to_null.wren
@@ -1,6 +1,6 @@
 class Foo {
   construct new() {}
-  write { IO.print(_field) }
+  write { System.print(_field) }
 }
 
 Foo.new().write // expect: null
diff --git a/test/language/field/multiple.wren b/test/language/field/multiple.wren
index 4c6f7e45..6f61e489 100644
--- a/test/language/field/multiple.wren
+++ b/test/language/field/multiple.wren
@@ -10,11 +10,11 @@ class Foo {
   }
 
   write {
-    IO.print(_a)
-    IO.print(_b)
-    IO.print(_c)
-    IO.print(_d)
-    IO.print(_e)
+    System.print(_a)
+    System.print(_b)
+    System.print(_c)
+    System.print(_d)
+    System.print(_e)
   }
 }
 
diff --git a/test/language/field/nested_class.wren b/test/language/field/nested_class.wren
index f23fed32..403518c1 100644
--- a/test/language/field/nested_class.wren
+++ b/test/language/field/nested_class.wren
@@ -3,19 +3,19 @@ class Outer {
 
   method {
     _field = "outer"
-    IO.print(_field) // expect: outer
+    System.print(_field) // expect: outer
 
     class Inner {
       construct new() {}
 
       method {
         _field = "inner"
-        IO.print(_field) // expect: inner
+        System.print(_field) // expect: inner
       }
     }
 
     Inner.new().method
-    IO.print(_field) // expect: outer
+    System.print(_field) // expect: outer
   }
 }
 
diff --git a/test/language/field/object_reference.wren b/test/language/field/object_reference.wren
index 5f29fa62..4067684f 100644
--- a/test/language/field/object_reference.wren
+++ b/test/language/field/object_reference.wren
@@ -11,7 +11,7 @@ class Node {
       _left.write()
     }
 
-    IO.print(_value)
+    System.print(_value)
 
     if (_right is Node) {
       _right.write()
diff --git a/test/language/field/use_before_set.wren b/test/language/field/use_before_set.wren
index d5a56f65..dc0b51a1 100644
--- a/test/language/field/use_before_set.wren
+++ b/test/language/field/use_before_set.wren
@@ -1,6 +1,6 @@
 class Foo {
   construct new() {}
-  write { IO.print(_field) } // Compile a use of the field...
+  write { System.print(_field) } // Compile a use of the field...
   init { _field = "value" }  // ...before an assignment to it.
 }
 
diff --git a/test/language/for/close_over_loop_variable.wren b/test/language/for/close_over_loop_variable.wren
index 21e50d14..7f1a242a 100644
--- a/test/language/for/close_over_loop_variable.wren
+++ b/test/language/for/close_over_loop_variable.wren
@@ -1,7 +1,7 @@
 var list = []
 
 for (i in [1, 2, 3]) {
-  list.add(Fn.new { IO.print(i) })
+  list.add(Fn.new { System.print(i) })
 }
 
 for (f in list) f.call()
diff --git a/test/language/for/closure_in_body.wren b/test/language/for/closure_in_body.wren
index 1dcd20e2..a1bbaecf 100644
--- a/test/language/for/closure_in_body.wren
+++ b/test/language/for/closure_in_body.wren
@@ -2,7 +2,7 @@ var list = []
 
 for (i in [1, 2, 3]) {
   var j = i + 1
-  list.add(Fn.new { IO.print(j) })
+  list.add(Fn.new { System.print(j) })
 }
 
 for (f in list) f.call()
diff --git a/test/language/for/newline_after_for.wren b/test/language/for/newline_after_for.wren
index 9cc6527f..43fbd993 100644
--- a/test/language/for/newline_after_for.wren
+++ b/test/language/for/newline_after_for.wren
@@ -1,2 +1,2 @@
 for // expect error
-(i in [1, 2, 3]) IO.print(i)
+(i in [1, 2, 3]) System.print(i)
diff --git a/test/language/for/newline_before_in.wren b/test/language/for/newline_before_in.wren
index 5412c680..51264b54 100644
--- a/test/language/for/newline_before_in.wren
+++ b/test/language/for/newline_before_in.wren
@@ -1,2 +1,2 @@
 for (i // expect error
-  in [1]) IO.print(i)
+  in [1]) System.print(i)
diff --git a/test/language/for/only_evaluate_sequence_once.wren b/test/language/for/only_evaluate_sequence_once.wren
index 9053a4a5..e8d06c27 100644
--- a/test/language/for/only_evaluate_sequence_once.wren
+++ b/test/language/for/only_evaluate_sequence_once.wren
@@ -1,9 +1,9 @@
 var f = Fn.new {
-  IO.print("evaluate sequence")
+  System.print("evaluate sequence")
   return [1, 2, 3]
 }
 
-for (i in f.call()) IO.print(i)
+for (i in f.call()) System.print(i)
 // expect: evaluate sequence
 // expect: 1
 // expect: 2
diff --git a/test/language/for/return_closure.wren b/test/language/for/return_closure.wren
index 8643ef3f..cbb2dd3c 100644
--- a/test/language/for/return_closure.wren
+++ b/test/language/for/return_closure.wren
@@ -1,6 +1,6 @@
 var f = Fn.new {
   for (i in [1, 2, 3]) {
-    return Fn.new { IO.print(i) }
+    return Fn.new { System.print(i) }
   }
 }
 
diff --git a/test/language/for/return_inside.wren b/test/language/for/return_inside.wren
index 6e92f0b9..1640973a 100644
--- a/test/language/for/return_inside.wren
+++ b/test/language/for/return_inside.wren
@@ -4,5 +4,5 @@ var f = Fn.new {
   }
 }
 
-IO.print(f.call())
+System.print(f.call())
 // expect: 1
diff --git a/test/language/for/syntax.wren b/test/language/for/syntax.wren
index 3325ff2b..f4c2aa28 100644
--- a/test/language/for/syntax.wren
+++ b/test/language/for/syntax.wren
@@ -1,14 +1,14 @@
 // Single-expression body.
-for (i in [1]) IO.print(i)
+for (i in [1]) System.print(i)
 // expect: 1
 
 // Block body.
 for (i in [1]) {
-  IO.print(i)
+  System.print(i)
 }
 // expect: 1
 
 // Newline after "in".
 for (i in
-  [1]) IO.print(i)
+  [1]) System.print(i)
 // expect: 1
\ No newline at end of file
diff --git a/test/language/for/truth.wren b/test/language/for/truth.wren
index ffbfe2b1..72adae79 100644
--- a/test/language/for/truth.wren
+++ b/test/language/for/truth.wren
@@ -6,27 +6,27 @@ class Iter {
 
 // False and null are false.
 for (n in Iter.new(false)) {
-  IO.print("bad")
+  System.print("bad")
   break
 }
 
 for (n in Iter.new(null)) {
-  IO.print("bad")
+  System.print("bad")
   break
 }
 
 // Everything else is true.
 for (n in Iter.new(true)) {
-  IO.print("true") // expect: true
+  System.print("true") // expect: true
   break
 }
 
 for (n in Iter.new(0)) {
-  IO.print(0) // expect: 0
+  System.print(0) // expect: 0
   break
 }
 
 for (n in Iter.new("")) {
-  IO.print("string") // expect: string
+  System.print("string") // expect: string
   break
 }
diff --git a/test/language/function/empty_body.wren b/test/language/function/empty_body.wren
index 773dcfed..2354bc9c 100644
--- a/test/language/function/empty_body.wren
+++ b/test/language/function/empty_body.wren
@@ -1,2 +1,2 @@
 var f = Fn.new {}
-IO.print(f.call()) // expect: null
+System.print(f.call()) // expect: null
diff --git a/test/language/function/newline_body.wren b/test/language/function/newline_body.wren
index 9151ea2d..b6eb0ff5 100644
--- a/test/language/function/newline_body.wren
+++ b/test/language/function/newline_body.wren
@@ -1,4 +1,4 @@
 var f = Fn.new {
   // Hi.
 }
-IO.print(f.call()) // expect: null
+System.print(f.call()) // expect: null
diff --git a/test/language/function/newline_in_expression_block.wren b/test/language/function/newline_in_expression_block.wren
index 099905ed..9e14a314 100644
--- a/test/language/function/newline_in_expression_block.wren
+++ b/test/language/function/newline_in_expression_block.wren
@@ -1,2 +1,2 @@
-Fn.new { IO.print("ok") // expect error
+Fn.new { System.print("ok") // expect error
 }.call()
diff --git a/test/language/function/no_newline_before_close.wren b/test/language/function/no_newline_before_close.wren
index 060db9a8..00164bf7 100644
--- a/test/language/function/no_newline_before_close.wren
+++ b/test/language/function/no_newline_before_close.wren
@@ -1,2 +1,2 @@
 Fn.new {
-  IO.print("ok") } // expect error
\ No newline at end of file
+  System.print("ok") } // expect error
\ No newline at end of file
diff --git a/test/language/function/parameters.wren b/test/language/function/parameters.wren
index 98c79f88..78225c1f 100644
--- a/test/language/function/parameters.wren
+++ b/test/language/function/parameters.wren
@@ -1,50 +1,50 @@
 var f0 = Fn.new { 0 }
-IO.print(f0.call()) // expect: 0
+System.print(f0.call()) // expect: 0
 
 var f1 = Fn.new {|a| a }
-IO.print(f1.call(1)) // expect: 1
+System.print(f1.call(1)) // expect: 1
 
 var f2 = Fn.new {|a, b| a + b }
-IO.print(f2.call(1, 2)) // expect: 3
+System.print(f2.call(1, 2)) // expect: 3
 
 var f3 = Fn.new {|a, b, c| a + b + c }
-IO.print(f3.call(1, 2, 3)) // expect: 6
+System.print(f3.call(1, 2, 3)) // expect: 6
 
 var f4 = Fn.new {|a, b, c, d| a + b + c + d }
-IO.print(f4.call(1, 2, 3, 4)) // expect: 10
+System.print(f4.call(1, 2, 3, 4)) // expect: 10
 
 var f5 = Fn.new {|a, b, c, d, e| a + b + c + d + e }
-IO.print(f5.call(1, 2, 3, 4, 5)) // expect: 15
+System.print(f5.call(1, 2, 3, 4, 5)) // expect: 15
 
 var f6 = Fn.new {|a, b, c, d, e, f| a + b + c + d + e + f }
-IO.print(f6.call(1, 2, 3, 4, 5, 6)) // expect: 21
+System.print(f6.call(1, 2, 3, 4, 5, 6)) // expect: 21
 
 var f7 = Fn.new {|a, b, c, d, e, f, g| a + b + c + d + e + f + g }
-IO.print(f7.call(1, 2, 3, 4, 5, 6, 7)) // expect: 28
+System.print(f7.call(1, 2, 3, 4, 5, 6, 7)) // expect: 28
 
 var f8 = Fn.new {|a, b, c, d, e, f, g, h| a + b + c + d + e + f + g + h }
-IO.print(f8.call(1, 2, 3, 4, 5, 6, 7, 8)) // expect: 36
+System.print(f8.call(1, 2, 3, 4, 5, 6, 7, 8)) // expect: 36
 
 var f9 = Fn.new {|a, b, c, d, e, f, g, h, i| a + b + c + d + e + f + g + h + i }
-IO.print(f9.call(1, 2, 3, 4, 5, 6, 7, 8, 9)) // expect: 45
+System.print(f9.call(1, 2, 3, 4, 5, 6, 7, 8, 9)) // expect: 45
 
 var f10 = Fn.new {|a, b, c, d, e, f, g, h, i, j| a + b + c + d + e + f + g + h + i + j }
-IO.print(f10.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)) // expect: 55
+System.print(f10.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)) // expect: 55
 
 var f11 = Fn.new {|a, b, c, d, e, f, g, h, i, j, k| a + b + c + d + e + f + g + h + i + j + k }
-IO.print(f11.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11)) // expect: 66
+System.print(f11.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11)) // expect: 66
 
 var f12 = Fn.new {|a, b, c, d, e, f, g, h, i, j, k, l| a + b + c + d + e + f + g + h + i + j + k + l }
-IO.print(f12.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)) // expect: 78
+System.print(f12.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)) // expect: 78
 
 var f13 = Fn.new {|a, b, c, d, e, f, g, h, i, j, k, l, m| a + b + c + d + e + f + g + h + i + j + k + l + m }
-IO.print(f13.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)) // expect: 91
+System.print(f13.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)) // expect: 91
 
 var f14 = Fn.new {|a, b, c, d, e, f, g, h, i, j, k, l, m, n| a + b + c + d + e + f + g + h + i + j + k + l + m + n }
-IO.print(f14.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)) // expect: 105
+System.print(f14.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)) // expect: 105
 
 var f15 = Fn.new {|a, b, c, d, e, f, g, h, i, j, k, l, m, n, o| a + b + c + d + e + f + g + h + i + j + k + l + m + n + o }
-IO.print(f15.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)) // expect: 120
+System.print(f15.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)) // expect: 120
 
 var f16 = Fn.new {|a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p| a + b + c + d + e + f + g + h + i + j + k + l + m + n + o + p }
-IO.print(f16.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)) // expect: 136
+System.print(f16.call(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)) // expect: 136
diff --git a/test/language/function/syntax.wren b/test/language/function/syntax.wren
index 2672d6be..8e94c2ca 100644
--- a/test/language/function/syntax.wren
+++ b/test/language/function/syntax.wren
@@ -1,25 +1,25 @@
 // Single expression body.
-Fn.new { IO.print("ok") }.call() // expect: ok
+Fn.new { System.print("ok") }.call() // expect: ok
 
 // Curly body.
 Fn.new {
-  IO.print("ok") // expect: ok
+  System.print("ok") // expect: ok
 }.call()
 
 // Multiple statements.
 Fn.new {
-  IO.print("1") // expect: 1
-  IO.print("2") // expect: 2
+  System.print("1") // expect: 1
+  System.print("2") // expect: 2
 }.call()
 
 // Extra newlines.
 Fn.new {
 
 
-  IO.print("1") // expect: 1
+  System.print("1") // expect: 1
 
 
-  IO.print("2") // expect: 2
+  System.print("2") // expect: 2
 
 
 }.call()
diff --git a/test/language/if/dangling_else.wren b/test/language/if/dangling_else.wren
index a1c50de8..d831be98 100644
--- a/test/language/if/dangling_else.wren
+++ b/test/language/if/dangling_else.wren
@@ -1,3 +1,3 @@
 // A dangling else binds to the right-most if.
-if (true) if (false) IO.print("bad") else IO.print("good") // expect: good
-if (false) if (true) IO.print("bad") else IO.print("bad")
+if (true) if (false) System.print("bad") else System.print("good") // expect: good
+if (false) if (true) System.print("bad") else System.print("bad")
diff --git a/test/language/if/else.wren b/test/language/if/else.wren
index 69a9914e..2fa42a2a 100644
--- a/test/language/if/else.wren
+++ b/test/language/if/else.wren
@@ -1,6 +1,6 @@
 // Evaluate the 'else' expression if the condition is false.
-if (true) IO.print("good") else IO.print("bad") // expect: good
-if (false) IO.print("bad") else IO.print("good") // expect: good
+if (true) System.print("good") else System.print("bad") // expect: good
+if (false) System.print("bad") else System.print("good") // expect: good
 
 // Allow block body.
-if (false) null else { IO.print("block") } // expect: block
+if (false) null else { System.print("block") } // expect: block
diff --git a/test/language/if/if.wren b/test/language/if/if.wren
index 11e5e0ea..3dd98358 100644
--- a/test/language/if/if.wren
+++ b/test/language/if/if.wren
@@ -1,10 +1,10 @@
 // Evaluate the 'then' expression if the condition is true.
-if (true) IO.print("good") // expect: good
-if (false) IO.print("bad")
+if (true) System.print("good") // expect: good
+if (false) System.print("bad")
 
 // Allow block body.
-if (true) { IO.print("block") } // expect: block
+if (true) { System.print("block") } // expect: block
 
 // Assignment in if condition.
 var a = false
-if (a = true) IO.print(a) // expect: true
+if (a = true) System.print(a) // expect: true
diff --git a/test/language/if/newline_after_if.wren b/test/language/if/newline_after_if.wren
index 3a2e49fc..213af793 100644
--- a/test/language/if/newline_after_if.wren
+++ b/test/language/if/newline_after_if.wren
@@ -1,2 +1,2 @@
 if // expect error
-(true) IO.print("bad")
+(true) System.print("bad")
diff --git a/test/language/if/truth.wren b/test/language/if/truth.wren
index 57e2a038..ad4964b2 100644
--- a/test/language/if/truth.wren
+++ b/test/language/if/truth.wren
@@ -1,8 +1,8 @@
 // False and null are false.
-if (false) IO.print("bad") else IO.print("false") // expect: false
-if (null) IO.print("bad") else IO.print("null") // expect: null
+if (false) System.print("bad") else System.print("false") // expect: false
+if (null) System.print("bad") else System.print("null") // expect: null
 
 // Everything else is true.
-if (true) IO.print(true) // expect: true
-if (0) IO.print(0) // expect: 0
-if ("") IO.print("empty") // expect: empty
+if (true) System.print(true) // expect: true
+if (0) System.print(0) // expect: 0
+if ("") System.print("empty") // expect: empty
diff --git a/test/language/ignore_carriage_returns.wren b/test/language/ignore_carriage_returns.wren
index 79e2968f..2de5f7ad 100644
--- a/test/language/ignore_carriage_returns.wren
+++ b/test/language/ignore_carriage_returns.wren
@@ -1,6 +1,6 @@
 // Sprinkle some carriage returns to ensure they are ignored anywhere:
-IO
.print("one"
)
-IO.print
("two")
+System
.print("one"
)
+System.print
("two")
 
 // Generate a compile error so we can test that the line number is correct.
 + * // expect error
diff --git a/test/language/implicit_receiver/inherited_methods.wren b/test/language/implicit_receiver/inherited_methods.wren
index 12888cc7..319b5c13 100644
--- a/test/language/implicit_receiver/inherited_methods.wren
+++ b/test/language/implicit_receiver/inherited_methods.wren
@@ -2,15 +2,15 @@ class Foo {
   construct new() {}
 
   getter {
-    IO.print("getter")
+    System.print("getter")
   }
 
   setter=(value) {
-    IO.print("setter")
+    System.print("setter")
   }
 
   method(a) {
-    IO.print("method")
+    System.print("method")
   }
 }
 
diff --git a/test/language/implicit_receiver/instance_methods.wren b/test/language/implicit_receiver/instance_methods.wren
index a3e5ab13..b07afbb1 100644
--- a/test/language/implicit_receiver/instance_methods.wren
+++ b/test/language/implicit_receiver/instance_methods.wren
@@ -2,15 +2,15 @@ class Foo {
   construct new() {}
 
   getter {
-    IO.print("getter")
+    System.print("getter")
   }
 
   setter=(value) {
-    IO.print("setter")
+    System.print("setter")
   }
 
   method(a) {
-    IO.print("method")
+    System.print("method")
   }
 
   test {
diff --git a/test/language/implicit_receiver/locals_shadow_getter.wren b/test/language/implicit_receiver/locals_shadow_getter.wren
index f04ef590..71827782 100644
--- a/test/language/implicit_receiver/locals_shadow_getter.wren
+++ b/test/language/implicit_receiver/locals_shadow_getter.wren
@@ -4,15 +4,15 @@ class Foo {
   bar { "getter" }
 
   test {
-    IO.print(bar) // expect: getter
+    System.print(bar) // expect: getter
 
     {
-      IO.print(bar) // expect: getter
+      System.print(bar) // expect: getter
       var bar = "local"
-      IO.print(bar) // expect: local
+      System.print(bar) // expect: local
     }
 
-    IO.print(bar) // expect: getter
+    System.print(bar) // expect: getter
   }
 }
 
diff --git a/test/language/implicit_receiver/locals_shadow_setter.wren b/test/language/implicit_receiver/locals_shadow_setter.wren
index 56bea7c7..ee084940 100644
--- a/test/language/implicit_receiver/locals_shadow_setter.wren
+++ b/test/language/implicit_receiver/locals_shadow_setter.wren
@@ -2,7 +2,7 @@ class Foo {
   construct new() {}
 
   bar=(value) {
-    IO.print("setter")
+    System.print("setter")
     return value
   }
 
diff --git a/test/language/implicit_receiver/nested_class.wren b/test/language/implicit_receiver/nested_class.wren
index 738447b9..eef0cf34 100644
--- a/test/language/implicit_receiver/nested_class.wren
+++ b/test/language/implicit_receiver/nested_class.wren
@@ -2,15 +2,15 @@ class Outer {
   construct new() {}
 
   getter {
-    IO.print("outer getter")
+    System.print("outer getter")
   }
 
   setter=(value) {
-    IO.print("outer setter")
+    System.print("outer setter")
   }
 
   method(a) {
-    IO.print("outer method")
+    System.print("outer method")
   }
 
   test {
@@ -22,15 +22,15 @@ class Outer {
       construct new() {}
 
       getter {
-        IO.print("inner getter")
+        System.print("inner getter")
       }
 
       setter=(value) {
-        IO.print("inner setter")
+        System.print("inner setter")
       }
 
       method(a) {
-        IO.print("inner method")
+        System.print("inner method")
       }
 
       test {
diff --git a/test/language/implicit_receiver/static_methods.wren b/test/language/implicit_receiver/static_methods.wren
index 95631ca8..4309c11c 100644
--- a/test/language/implicit_receiver/static_methods.wren
+++ b/test/language/implicit_receiver/static_methods.wren
@@ -1,14 +1,14 @@
 class Foo {
   static getter {
-    IO.print("getter")
+    System.print("getter")
   }
 
   static setter=(value) {
-    IO.print("setter")
+    System.print("setter")
   }
 
   static method(a) {
-    IO.print("method")
+    System.print("method")
   }
 
   static test {
diff --git a/test/language/inheritance/do_not_inherit_static_methods.wren b/test/language/inheritance/do_not_inherit_static_methods.wren
index 36da1395..279ca172 100644
--- a/test/language/inheritance/do_not_inherit_static_methods.wren
+++ b/test/language/inheritance/do_not_inherit_static_methods.wren
@@ -1,5 +1,5 @@
 class Foo {
-  static methodOnFoo { IO.print("foo") }
+  static methodOnFoo { System.print("foo") }
 }
 
 class Bar is Foo {}
diff --git a/test/language/inheritance/inherit_fields.wren b/test/language/inheritance/inherit_fields.wren
index d25e1e38..6c1be664 100644
--- a/test/language/inheritance/inherit_fields.wren
+++ b/test/language/inheritance/inherit_fields.wren
@@ -7,8 +7,8 @@ class Foo {
   }
 
   fooPrint {
-    IO.print(_field1)
-    IO.print(_field2)
+    System.print(_field1)
+    System.print(_field2)
   }
 }
 
@@ -21,8 +21,8 @@ class Bar is Foo {
   }
 
   barPrint {
-    IO.print(_field1)
-    IO.print(_field2)
+    System.print(_field1)
+    System.print(_field2)
   }
 }
 
diff --git a/test/language/inheritance/inherit_from_closure.wren b/test/language/inheritance/inherit_from_closure.wren
index c79e8d01..acb4eeab 100644
--- a/test/language/inheritance/inherit_from_closure.wren
+++ b/test/language/inheritance/inherit_from_closure.wren
@@ -2,7 +2,7 @@ var ClosureType
 
 {
   var a = "a"
-  ClosureType = Fn.new { IO.print(a) }.type
+  ClosureType = Fn.new { System.print(a) }.type
 }
 
 class Subclass is ClosureType {} // expect runtime error: Class 'Subclass' cannot inherit from built-in class 'Fn'.
diff --git a/test/language/inheritance/inherit_methods.wren b/test/language/inheritance/inherit_methods.wren
index d71b696b..fda31b8e 100644
--- a/test/language/inheritance/inherit_methods.wren
+++ b/test/language/inheritance/inherit_methods.wren
@@ -1,16 +1,16 @@
 class Foo {
-  methodOnFoo { IO.print("foo") }
-  method(a) { IO.print("foo") }
-  method(a, b, c) { IO.print("foo") }
-  override { IO.print("foo") }
+  methodOnFoo { System.print("foo") }
+  method(a) { System.print("foo") }
+  method(a, b, c) { System.print("foo") }
+  override { System.print("foo") }
 }
 
 class Bar is Foo {
   construct new() {}
-  methodOnBar { IO.print("bar") }
-  method(a, b) { IO.print("bar") }
-  method(a, b, c, d) { IO.print("bar") }
-  override { IO.print("bar") }
+  methodOnBar { System.print("bar") }
+  method(a, b) { System.print("bar") }
+  method(a, b, c, d) { System.print("bar") }
+  override { System.print("bar") }
 }
 
 var bar = Bar.new()
diff --git a/test/language/inheritance/inherited_fields_in_closure.wren b/test/language/inheritance/inherited_fields_in_closure.wren
index c9e8bfb1..3dddf275 100644
--- a/test/language/inheritance/inherited_fields_in_closure.wren
+++ b/test/language/inheritance/inherited_fields_in_closure.wren
@@ -26,11 +26,11 @@ class Bar is Foo {
 }
 
 var bar = Bar.new()
-IO.print(bar.closeOverFooGet.call().call()) // expect: Foo field
-IO.print(bar.closeOverBarGet.call().call()) // expect: Bar field
+System.print(bar.closeOverFooGet.call().call()) // expect: Foo field
+System.print(bar.closeOverBarGet.call().call()) // expect: Bar field
 bar.closeOverFooSet.call().call()
-IO.print(bar.closeOverFooGet.call().call()) // expect: new foo value
-IO.print(bar.closeOverBarGet.call().call()) // expect: Bar field
+System.print(bar.closeOverFooGet.call().call()) // expect: new foo value
+System.print(bar.closeOverBarGet.call().call()) // expect: Bar field
 bar.closeOverBarSet.call().call()
-IO.print(bar.closeOverFooGet.call().call()) // expect: new foo value
-IO.print(bar.closeOverBarGet.call().call()) // expect: new bar value
+System.print(bar.closeOverFooGet.call().call()) // expect: new foo value
+System.print(bar.closeOverBarGet.call().call()) // expect: new bar value
diff --git a/test/language/inheritance/is.wren b/test/language/inheritance/is.wren
index d07d776a..f8c73850 100644
--- a/test/language/inheritance/is.wren
+++ b/test/language/inheritance/is.wren
@@ -11,12 +11,12 @@ var a = A.new()
 var b = B.new()
 var c = C.new()
 
-IO.print(a is A) // expect: true
-IO.print(a is B) // expect: false
-IO.print(a is C) // expect: false
-IO.print(b is A) // expect: true
-IO.print(b is B) // expect: true
-IO.print(b is C) // expect: false
-IO.print(c is A) // expect: true
-IO.print(c is B) // expect: true
-IO.print(c is C) // expect: true
+System.print(a is A) // expect: true
+System.print(a is B) // expect: false
+System.print(a is C) // expect: false
+System.print(b is A) // expect: true
+System.print(b is B) // expect: true
+System.print(b is C) // expect: false
+System.print(c is A) // expect: true
+System.print(c is B) // expect: true
+System.print(c is C) // expect: true
diff --git a/test/language/is/is.wren b/test/language/is/is.wren
index fe4c41ff..e367636d 100644
--- a/test/language/is/is.wren
+++ b/test/language/is/is.wren
@@ -1,33 +1,33 @@
-IO.print(Num is Class) // expect: true
-IO.print(true is Bool) // expect: true
-IO.print(Fn.new { 1 } is Fn) // expect: true
-IO.print(123 is Num) // expect: true
-IO.print(null is Null) // expect: true
-IO.print("s" is String) // expect: true
+System.print(Num is Class) // expect: true
+System.print(true is Bool) // expect: true
+System.print(Fn.new { 1 } is Fn) // expect: true
+System.print(123 is Num) // expect: true
+System.print(null is Null) // expect: true
+System.print("s" is String) // expect: true
 
-IO.print(Num is Bool) // expect: false
-IO.print(null is Class) // expect: false
-IO.print(true is Fn) // expect: false
-IO.print(Fn.new { 1 } is Num) // expect: false
-IO.print("s" is Null) // expect: false
-IO.print(123 is String) // expect: false
+System.print(Num is Bool) // expect: false
+System.print(null is Class) // expect: false
+System.print(true is Fn) // expect: false
+System.print(Fn.new { 1 } is Num) // expect: false
+System.print("s" is Null) // expect: false
+System.print(123 is String) // expect: false
 
 // Everything extends Object.
-IO.print(Num is Object) // expect: true
-IO.print(null is Object) // expect: true
-IO.print(true is Object) // expect: true
-IO.print(Fn.new { 1 } is Object) // expect: true
-IO.print("s" is Object) // expect: true
-IO.print(123 is Object) // expect: true
+System.print(Num is Object) // expect: true
+System.print(null is Object) // expect: true
+System.print(true is Object) // expect: true
+System.print(Fn.new { 1 } is Object) // expect: true
+System.print("s" is Object) // expect: true
+System.print(123 is Object) // expect: true
 
 // Classes extend Class.
-IO.print(Num is Class) // expect: true
-IO.print(null is Class) // expect: false
-IO.print(true is Class) // expect: false
-IO.print(Fn.new { 1 } is Class) // expect: false
-IO.print("s" is Class) // expect: false
-IO.print(123 is Class) // expect: false
+System.print(Num is Class) // expect: true
+System.print(null is Class) // expect: false
+System.print(true is Class) // expect: false
+System.print(Fn.new { 1 } is Class) // expect: false
+System.print("s" is Class) // expect: false
+System.print(123 is Class) // expect: false
 
 // Ignore newline after "is".
-IO.print(123 is
+System.print(123 is
   Num) // expect: true
\ No newline at end of file
diff --git a/test/language/list/grow_shrink.wren b/test/language/list/grow_shrink.wren
index a1e9fd58..fc06fb54 100644
--- a/test/language/list/grow_shrink.wren
+++ b/test/language/list/grow_shrink.wren
@@ -8,4 +8,4 @@ for (i in 0..195) {
   list.removeAt(-1)
 }
 
-IO.print(list) // expect: [0, 1, 2, 3, 4]
+System.print(list) // expect: [0, 1, 2, 3, 4]
diff --git a/test/language/list/newlines.wren b/test/language/list/newlines.wren
index 61296116..f8d49b0e 100644
--- a/test/language/list/newlines.wren
+++ b/test/language/list/newlines.wren
@@ -6,19 +6,19 @@ var list = [
 
 ]
 
-IO.print(list[0]) // expect: a
-IO.print(list[1]) // expect: b
+System.print(list[0]) // expect: a
+System.print(list[1]) // expect: b
 
 // Newline after trailing comma.
 list = ["c",
 
 ]
 
-IO.print(list[0]) // expect: c
+System.print(list[0]) // expect: c
 
 // Newline in empty list.
 list = [
 
 ]
 
-IO.print(list.count) // expect: 0
+System.print(list.count) // expect: 0
diff --git a/test/language/list/trailing_comma.wren b/test/language/list/trailing_comma.wren
index e6f64348..66965555 100644
--- a/test/language/list/trailing_comma.wren
+++ b/test/language/list/trailing_comma.wren
@@ -1,4 +1,4 @@
 var list = ["a", "b",]
 
-IO.print(list[0]) // expect: a
-IO.print(list[1]) // expect: b
+System.print(list[0]) // expect: a
+System.print(list[1]) // expect: b
diff --git a/test/language/logical_operator/and.wren b/test/language/logical_operator/and.wren
index db8c9618..1b793afb 100644
--- a/test/language/logical_operator/and.wren
+++ b/test/language/logical_operator/and.wren
@@ -1,20 +1,20 @@
 // Note: These tests implicitly depend on ints being truthy.
-//       Also rely on IO.print() returning its argument.
+//       Also rely on System.print() returning its argument.
 
 // Return the first non-true argument.
-IO.print(false && 1) // expect: false
-IO.print(true && 1) // expect: 1
-IO.print(1 && 2 && false) // expect: false
+System.print(false && 1) // expect: false
+System.print(true && 1) // expect: 1
+System.print(1 && 2 && false) // expect: false
 
 // Return the last argument if all are true.
-IO.print(1 && true) // expect: true
-IO.print(1 && 2 && 3) // expect: 3
+System.print(1 && true) // expect: true
+System.print(1 && 2 && 3) // expect: 3
 
 // Short-circuit at the first false argument.
-IO.print(true) && // expect: true
-    IO.print(false) && // expect: false
-    IO.print(false) // should not print
+System.print(true) && // expect: true
+    System.print(false) && // expect: false
+    System.print(false) // should not print
 
 // Swallow a trailing newline.
-IO.print(true &&
+System.print(true &&
     true) // expect: true
diff --git a/test/language/logical_operator/and_truth.wren b/test/language/logical_operator/and_truth.wren
index 4c4e365a..deef46a1 100644
--- a/test/language/logical_operator/and_truth.wren
+++ b/test/language/logical_operator/and_truth.wren
@@ -1,8 +1,8 @@
 // False and null are false.
-IO.print(false && "bad") // expect: false
-IO.print(null && "bad") // expect: null
+System.print(false && "bad") // expect: false
+System.print(null && "bad") // expect: null
 
 // Everything else is true.
-IO.print(true && "ok") // expect: ok
-IO.print(0 && "ok") // expect: ok
-IO.print("" && "ok") // expect: ok
+System.print(true && "ok") // expect: ok
+System.print(0 && "ok") // expect: ok
+System.print("" && "ok") // expect: ok
diff --git a/test/language/logical_operator/or.wren b/test/language/logical_operator/or.wren
index 3e4779e3..6645f1bf 100644
--- a/test/language/logical_operator/or.wren
+++ b/test/language/logical_operator/or.wren
@@ -1,20 +1,20 @@
 // Note: These tests implicitly depend on ints being truthy.
-//       Also rely on IO.print() returning its argument.
+//       Also rely on System.print() returning its argument.
 
 // Return the first true argument.
-IO.print(1 || true) // expect: 1
-IO.print(false || 1) // expect: 1
-IO.print(false || false || true) // expect: true
+System.print(1 || true) // expect: 1
+System.print(false || 1) // expect: 1
+System.print(false || false || true) // expect: true
 
 // Return the last argument if all are false.
-IO.print(false || false) // expect: false
-IO.print(false || false || false) // expect: false
+System.print(false || false) // expect: false
+System.print(false || false || false) // expect: false
 
 // Short-circuit at the first true argument.
-IO.print(false) || // expect: false
-    IO.print(true) || // expect: true
-    IO.print(true) // should not print
+System.print(false) || // expect: false
+    System.print(true) || // expect: true
+    System.print(true) // should not print
 
 // Swallow a trailing newline.
-IO.print(true ||
+System.print(true ||
     true) // expect: true
diff --git a/test/language/logical_operator/or_truth.wren b/test/language/logical_operator/or_truth.wren
index fd6aa2fc..e7f39e26 100644
--- a/test/language/logical_operator/or_truth.wren
+++ b/test/language/logical_operator/or_truth.wren
@@ -1,8 +1,8 @@
 // False and null are false.
-IO.print(false || "ok") // expect: ok
-IO.print(null || "ok") // expect: ok
+System.print(false || "ok") // expect: ok
+System.print(null || "ok") // expect: ok
 
 // Everything else is true.
-IO.print(true || "ok") // expect: true
-IO.print(0 || "ok") // expect: 0
-IO.print("s" || "ok") // expect: s
+System.print(true || "ok") // expect: true
+System.print(0 || "ok") // expect: 0
+System.print("s" || "ok") // expect: s
diff --git a/test/language/map/grow_and_shrink.wren b/test/language/map/grow_and_shrink.wren
index a43c9b05..09dd3f34 100644
--- a/test/language/map/grow_and_shrink.wren
+++ b/test/language/map/grow_and_shrink.wren
@@ -64,13 +64,13 @@ for (fish in fishes) {
   map[fish] = fish.count
 }
 
-IO.print(map.count) // expect: 249
+System.print(map.count) // expect: 249
 
 for (n in 0...150) {
   map.remove(fishes[n])
 }
 
-IO.print(map.count) // expect: 99
+System.print(map.count) // expect: 99
 
 // Make sure we can still find all of the remaining ones.
 var contained = 0
@@ -78,4 +78,4 @@ for (n in 150...249) {
   if (map.containsKey(fishes[n])) contained = contained + 1
 }
 
-IO.print(contained) // expect: 99
+System.print(contained) // expect: 99
diff --git a/test/language/map/newlines.wren b/test/language/map/newlines.wren
index c61e81b0..e6d48cb0 100644
--- a/test/language/map/newlines.wren
+++ b/test/language/map/newlines.wren
@@ -9,19 +9,19 @@ var map = {
 
 }
 
-IO.print(map["a"]) // expect: a value
-IO.print(map["b"]) // expect: b value
+System.print(map["a"]) // expect: a value
+System.print(map["b"]) // expect: b value
 
 // Newline after trailing comma.
 map = {"c": "c value",
 
 }
 
-IO.print(map["c"]) // expect: c value
+System.print(map["c"]) // expect: c value
 
 // Newline in empty map.
 map = {
 
 }
 
-IO.print(map.count) // expect: 0
+System.print(map.count) // expect: 0
diff --git a/test/language/map/trailing_comma.wren b/test/language/map/trailing_comma.wren
index 7dd0a69f..298f7b02 100644
--- a/test/language/map/trailing_comma.wren
+++ b/test/language/map/trailing_comma.wren
@@ -3,5 +3,5 @@ var map = {
   "b": 2,
 }
 
-IO.print(map["a"]) // expect: 1
-IO.print(map["b"]) // expect: 2
+System.print(map["a"]) // expect: 1
+System.print(map["b"]) // expect: 2
diff --git a/test/language/method/arity.wren b/test/language/method/arity.wren
index 987de59f..9501f330 100644
--- a/test/language/method/arity.wren
+++ b/test/language/method/arity.wren
@@ -21,21 +21,21 @@ class Foo {
 }
 
 var foo = Foo.new()
-IO.print(foo.method) // expect: getter
-IO.print(foo.method()) // expect: no args
-IO.print(foo.method(1)) // expect: 1
-IO.print(foo.method(1, 2)) // expect: 3
-IO.print(foo.method(1, 2, 3)) // expect: 6
-IO.print(foo.method(1, 2, 3, 4)) // expect: 10
-IO.print(foo.method(1, 2, 3, 4, 5)) // expect: 15
-IO.print(foo.method(1, 2, 3, 4, 5, 6)) // expect: 21
-IO.print(foo.method(1, 2, 3, 4, 5, 6, 7)) // expect: 28
-IO.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8)) // expect: 36
-IO.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9)) // expect: 45
-IO.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)) // expect: 55
-IO.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11)) // expect: 66
-IO.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)) // expect: 78
-IO.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)) // expect: 91
-IO.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)) // expect: 105
-IO.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)) // expect: 120
-IO.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)) // expect: 136
+System.print(foo.method) // expect: getter
+System.print(foo.method()) // expect: no args
+System.print(foo.method(1)) // expect: 1
+System.print(foo.method(1, 2)) // expect: 3
+System.print(foo.method(1, 2, 3)) // expect: 6
+System.print(foo.method(1, 2, 3, 4)) // expect: 10
+System.print(foo.method(1, 2, 3, 4, 5)) // expect: 15
+System.print(foo.method(1, 2, 3, 4, 5, 6)) // expect: 21
+System.print(foo.method(1, 2, 3, 4, 5, 6, 7)) // expect: 28
+System.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8)) // expect: 36
+System.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9)) // expect: 45
+System.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)) // expect: 55
+System.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11)) // expect: 66
+System.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)) // expect: 78
+System.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)) // expect: 91
+System.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)) // expect: 105
+System.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)) // expect: 120
+System.print(foo.method(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)) // expect: 136
diff --git a/test/language/method/empty_block.wren b/test/language/method/empty_block.wren
index 70dba5ba..e1a75265 100644
--- a/test/language/method/empty_block.wren
+++ b/test/language/method/empty_block.wren
@@ -3,4 +3,4 @@ class Foo {
   bar {}
 }
 
-IO.print(Foo.new().bar) // expect: null
+System.print(Foo.new().bar) // expect: null
diff --git a/test/language/method/long_name.wren b/test/language/method/long_name.wren
index 83cb6e7f..db18373a 100644
--- a/test/language/method/long_name.wren
+++ b/test/language/method/long_name.wren
@@ -5,4 +5,4 @@ class Foo {
   }
 }
 
-IO.print(Foo.new().thisHasAMethodNameThatIsExactly64CharactersLongWhichIsTheMaximum) // expect: result
+System.print(Foo.new().thisHasAMethodNameThatIsExactly64CharactersLongWhichIsTheMaximum) // expect: result
diff --git a/test/language/method/many_methods.wren b/test/language/method/many_methods.wren
index adc69b0b..57994926 100644
--- a/test/language/method/many_methods.wren
+++ b/test/language/method/many_methods.wren
@@ -2022,4 +2022,4 @@ result = result + foo.method996
 result = result + foo.method997
 result = result + foo.method998
 result = result + foo.method999
-IO.print(result) // expect: 1000
+System.print(result) // expect: 1000
diff --git a/test/language/method/newlines.wren b/test/language/method/newlines.wren
index 0f9225e9..33b41def 100644
--- a/test/language/method/newlines.wren
+++ b/test/language/method/newlines.wren
@@ -7,14 +7,14 @@ class Foo {
 var foo = Foo.new()
 
 // Allow newlines after commas and before ")".
-IO.print(foo.method("a",
+System.print(foo.method("a",
 
     "b"
 
     )) // expect: method a b
 
 // Allow newlines after commas and before "]".
-IO.print(foo["a",
+System.print(foo["a",
 
     "b"
 
diff --git a/test/language/method/operators.wren b/test/language/method/operators.wren
index 53934f51..e36e306f 100644
--- a/test/language/method/operators.wren
+++ b/test/language/method/operators.wren
@@ -21,19 +21,19 @@ class Foo {
 }
 
 var foo = Foo.new()
-IO.print(foo + "a") // expect: infix + a
-IO.print(foo - "a") // expect: infix - a
-IO.print(foo * "a") // expect: infix * a
-IO.print(foo / "a") // expect: infix / a
-IO.print(foo % "a") // expect: infix % a
-IO.print(foo < "a") // expect: infix < a
-IO.print(foo > "a") // expect: infix > a
-IO.print(foo <= "a") // expect: infix <= a
-IO.print(foo >= "a") // expect: infix >= a
-IO.print(foo == "a") // expect: infix == a
-IO.print(foo != "a") // expect: infix != a
-IO.print(foo & "a") // expect: infix & a
-IO.print(foo | "a") // expect: infix | a
-IO.print(!foo) // expect: prefix !
-IO.print(~foo) // expect: prefix ~
-IO.print(-foo) // expect: prefix -
+System.print(foo + "a") // expect: infix + a
+System.print(foo - "a") // expect: infix - a
+System.print(foo * "a") // expect: infix * a
+System.print(foo / "a") // expect: infix / a
+System.print(foo % "a") // expect: infix % a
+System.print(foo < "a") // expect: infix < a
+System.print(foo > "a") // expect: infix > a
+System.print(foo <= "a") // expect: infix <= a
+System.print(foo >= "a") // expect: infix >= a
+System.print(foo == "a") // expect: infix == a
+System.print(foo != "a") // expect: infix != a
+System.print(foo & "a") // expect: infix & a
+System.print(foo | "a") // expect: infix | a
+System.print(!foo) // expect: prefix !
+System.print(~foo) // expect: prefix ~
+System.print(-foo) // expect: prefix -
diff --git a/test/language/method/static.wren b/test/language/method/static.wren
index bdf4984c..0921779e 100644
--- a/test/language/method/static.wren
+++ b/test/language/method/static.wren
@@ -7,7 +7,7 @@ class Foo {
   static bar(arg) { "on metaclass " + arg }
 }
 
-IO.print(Foo.new().bar)        // expect: on instance
-IO.print(Foo.bar)              // expect: on metaclass
-IO.print(Foo.new().bar("arg")) // expect: on instance arg
-IO.print(Foo.bar("arg"))       // expect: on metaclass arg
+System.print(Foo.new().bar)        // expect: on instance
+System.print(Foo.bar)              // expect: on metaclass
+System.print(Foo.new().bar("arg")) // expect: on instance arg
+System.print(Foo.bar("arg"))       // expect: on metaclass arg
diff --git a/test/language/method/subscript_operators.wren b/test/language/method/subscript_operators.wren
index 57b6d4df..6ce5c1b4 100644
--- a/test/language/method/subscript_operators.wren
+++ b/test/language/method/subscript_operators.wren
@@ -9,9 +9,9 @@ class Foo {
 }
 
 var foo = Foo.new()
-IO.print(foo["a"]) // expect: 1-subscript a
-IO.print(foo["a", "b"]) // expect: 2-subscript a b
-IO.print(foo["a", "b", "c"]) // expect: 3-subscript a b c
-IO.print(foo["a"] = "value") // expect: 1-subscript setter a = value
-IO.print(foo["a", "b"] = "value") // expect: 2-subscript setter a b = value
-IO.print(foo["a", "b", "c"] = "value") // expect: 3-subscript setter a b c = value
+System.print(foo["a"]) // expect: 1-subscript a
+System.print(foo["a", "b"]) // expect: 2-subscript a b
+System.print(foo["a", "b", "c"]) // expect: 3-subscript a b c
+System.print(foo["a"] = "value") // expect: 1-subscript setter a = value
+System.print(foo["a", "b"] = "value") // expect: 2-subscript setter a b = value
+System.print(foo["a", "b", "c"] = "value") // expect: 3-subscript setter a b c = value
diff --git a/test/language/method/too_many_arguments.wren b/test/language/method/too_many_arguments.wren
index c49643b8..e49c76ba 100644
--- a/test/language/method/too_many_arguments.wren
+++ b/test/language/method/too_many_arguments.wren
@@ -1 +1 @@
-IO.print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17) // expect error
+System.print(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17) // expect error
diff --git a/test/language/module/change_imported_value/change_imported_value.wren b/test/language/module/change_imported_value/change_imported_value.wren
index c5163410..0f5aa0ff 100644
--- a/test/language/module/change_imported_value/change_imported_value.wren
+++ b/test/language/module/change_imported_value/change_imported_value.wren
@@ -1,11 +1,11 @@
 import "module" for Module, Other
 
-IO.print(Module) // expect: before
+System.print(Module) // expect: before
 
 // Reassigning the variable in the other module does not affect this one's
 // binding.
 Other.change
-IO.print(Module) // expect: before
+System.print(Module) // expect: before
 
 // But it does change there.
 Other.show // expect: after
diff --git a/test/language/module/change_imported_value/module.wren b/test/language/module/change_imported_value/module.wren
index fac9ddc9..8a6f9986 100644
--- a/test/language/module/change_imported_value/module.wren
+++ b/test/language/module/change_imported_value/module.wren
@@ -7,6 +7,6 @@ class Other {
   }
 
   static show {
-    IO.print(Module)
+    System.print(Module)
   }
 }
diff --git a/test/language/module/cyclic_import/a.wren b/test/language/module/cyclic_import/a.wren
index 08000a19..54e0a80d 100644
--- a/test/language/module/cyclic_import/a.wren
+++ b/test/language/module/cyclic_import/a.wren
@@ -1,9 +1,9 @@
 // nontest
-IO.print("start a")
+System.print("start a")
 
 var A = "a value"
-IO.print("a defined ", A)
+System.print("a defined " + A)
 import "b" for B
-IO.print("a imported ", B)
+System.print("a imported " + B)
 
-IO.print("end a")
\ No newline at end of file
+System.print("end a")
\ No newline at end of file
diff --git a/test/language/module/cyclic_import/b.wren b/test/language/module/cyclic_import/b.wren
index 3b049a50..3671f9d5 100644
--- a/test/language/module/cyclic_import/b.wren
+++ b/test/language/module/cyclic_import/b.wren
@@ -1,9 +1,9 @@
 // nontest
-IO.print("start b")
+System.print("start b")
 
 var B = "b value"
-IO.print("b defined ", B)
+System.print("b defined " + B)
 import "a" for A
-IO.print("b imported ", A)
+System.print("b imported " + A)
 
-IO.print("end b")
+System.print("end b")
diff --git a/test/language/module/implicitly_imports_core/module.wren b/test/language/module/implicitly_imports_core/module.wren
index bd444960..3f592932 100644
--- a/test/language/module/implicitly_imports_core/module.wren
+++ b/test/language/module/implicitly_imports_core/module.wren
@@ -1,15 +1,15 @@
 // nontest
-IO.print(Bool)
-IO.print(Class)
-IO.print(Fiber)
-IO.print(Fn)
-IO.print(List)
-IO.print(Map)
-IO.print(MapKeySequence)
-IO.print(MapValueSequence)
-IO.print(Null)
-IO.print(Num)
-IO.print(Object)
-IO.print(Range)
-IO.print(Sequence)
-IO.print(String)
+System.print(Bool)
+System.print(Class)
+System.print(Fiber)
+System.print(Fn)
+System.print(List)
+System.print(Map)
+System.print(MapKeySequence)
+System.print(MapValueSequence)
+System.print(Null)
+System.print(Num)
+System.print(Object)
+System.print(Range)
+System.print(Sequence)
+System.print(String)
diff --git a/test/language/module/inside_block/inside_block.wren b/test/language/module/inside_block/inside_block.wren
index d15d27d9..f19bc0c7 100644
--- a/test/language/module/inside_block/inside_block.wren
+++ b/test/language/module/inside_block/inside_block.wren
@@ -4,7 +4,7 @@ if (true) {
   import "module" for Module
   // expect: ran module
 
-  IO.print(Module) // expect: from module
+  System.print(Module) // expect: from module
 }
 
-IO.print(Module) // expect: outer
+System.print(Module) // expect: outer
diff --git a/test/language/module/inside_block/module.wren b/test/language/module/inside_block/module.wren
index cf2ce362..a1289a13 100644
--- a/test/language/module/inside_block/module.wren
+++ b/test/language/module/inside_block/module.wren
@@ -1,3 +1,3 @@
 // nontest
 var Module = "from module"
-IO.print("ran module")
+System.print("ran module")
diff --git a/test/language/module/module_dir/module_dir.wren b/test/language/module/module_dir/module_dir.wren
index a19d6ade..e2867d02 100644
--- a/test/language/module/module_dir/module_dir.wren
+++ b/test/language/module/module_dir/module_dir.wren
@@ -1,3 +1,3 @@
 import "something" for Index
 
-IO.print(Index) // expect: index
\ No newline at end of file
+System.print(Index) // expect: index
\ No newline at end of file
diff --git a/test/language/module/multiple_variables/module.wren b/test/language/module/multiple_variables/module.wren
index ed5932ca..85a562f7 100644
--- a/test/language/module/multiple_variables/module.wren
+++ b/test/language/module/multiple_variables/module.wren
@@ -5,4 +5,4 @@ var Module3 = "from module three"
 var Module4 = "from module four"
 var Module5 = "from module five"
 
-IO.print("ran module")
+System.print("ran module")
diff --git a/test/language/module/multiple_variables/multiple_variables.wren b/test/language/module/multiple_variables/multiple_variables.wren
index 7d007604..abf387c6 100644
--- a/test/language/module/multiple_variables/multiple_variables.wren
+++ b/test/language/module/multiple_variables/multiple_variables.wren
@@ -3,8 +3,8 @@ import "module" for Module1, Module2, Module3, Module4, Module5
 // Only execute module body once:
 // expect: ran module
 
-IO.print(Module1) // expect: from module one
-IO.print(Module2) // expect: from module two
-IO.print(Module3) // expect: from module three
-IO.print(Module4) // expect: from module four
-IO.print(Module5) // expect: from module five
+System.print(Module1) // expect: from module one
+System.print(Module2) // expect: from module two
+System.print(Module3) // expect: from module three
+System.print(Module4) // expect: from module four
+System.print(Module5) // expect: from module five
diff --git a/test/language/module/no_variable/module.wren b/test/language/module/no_variable/module.wren
index c1acca4a..e761fd73 100644
--- a/test/language/module/no_variable/module.wren
+++ b/test/language/module/no_variable/module.wren
@@ -1,2 +1,2 @@
 // nontest
-IO.print("ran module")
+System.print("ran module")
diff --git a/test/language/module/shared_import/a.wren b/test/language/module/shared_import/a.wren
index 658a34d3..96dd90a2 100644
--- a/test/language/module/shared_import/a.wren
+++ b/test/language/module/shared_import/a.wren
@@ -1,5 +1,5 @@
 // nontest
-IO.print("a")
+System.print("a")
 import "shared" for Shared
 var A = "a " + Shared
-IO.print("a done")
+System.print("a done")
diff --git a/test/language/module/shared_import/b.wren b/test/language/module/shared_import/b.wren
index 63753be1..7dd9f4ab 100644
--- a/test/language/module/shared_import/b.wren
+++ b/test/language/module/shared_import/b.wren
@@ -1,5 +1,5 @@
 // nontest
-IO.print("b")
+System.print("b")
 import "shared" for Shared
 var B = "b " + Shared
-IO.print("b done")
+System.print("b done")
diff --git a/test/language/module/shared_import/shared.wren b/test/language/module/shared_import/shared.wren
index cd67246c..e8250cd0 100644
--- a/test/language/module/shared_import/shared.wren
+++ b/test/language/module/shared_import/shared.wren
@@ -1,3 +1,3 @@
 // nontest
-IO.print("shared")
+System.print("shared")
 var Shared = "shared"
diff --git a/test/language/module/shared_import/shared_import.wren b/test/language/module/shared_import/shared_import.wren
index 0ff45b30..970cfe62 100644
--- a/test/language/module/shared_import/shared_import.wren
+++ b/test/language/module/shared_import/shared_import.wren
@@ -8,5 +8,5 @@ import "b" for B
 // expect: b
 // expect: b done
 
-IO.print(A) // expect: a shared
-IO.print(B) // expect: b shared
+System.print(A) // expect: a shared
+System.print(B) // expect: b shared
diff --git a/test/language/module/simple_import/module.wren b/test/language/module/simple_import/module.wren
index cf2ce362..a1289a13 100644
--- a/test/language/module/simple_import/module.wren
+++ b/test/language/module/simple_import/module.wren
@@ -1,3 +1,3 @@
 // nontest
 var Module = "from module"
-IO.print("ran module")
+System.print("ran module")
diff --git a/test/language/module/simple_import/simple_import.wren b/test/language/module/simple_import/simple_import.wren
index aae635ec..eb46932b 100644
--- a/test/language/module/simple_import/simple_import.wren
+++ b/test/language/module/simple_import/simple_import.wren
@@ -1,4 +1,4 @@
 import "module" for Module
 // expect: ran module
 
-IO.print(Module) // expect: from module
+System.print(Module) // expect: from module
diff --git a/test/language/module/unknown_variable/module.wren b/test/language/module/unknown_variable/module.wren
index cf2ce362..a1289a13 100644
--- a/test/language/module/unknown_variable/module.wren
+++ b/test/language/module/unknown_variable/module.wren
@@ -1,3 +1,3 @@
 // nontest
 var Module = "from module"
-IO.print("ran module")
+System.print("ran module")
diff --git a/test/language/no_trailing_newline.wren b/test/language/no_trailing_newline.wren
index 0b7bfa9e..c44c2d41 100644
--- a/test/language/no_trailing_newline.wren
+++ b/test/language/no_trailing_newline.wren
@@ -1 +1 @@
-IO.print("ok") // expect: ok
\ No newline at end of file
+System.print("ok") // expect: ok
\ No newline at end of file
diff --git a/test/language/nonlocal/assignment.wren b/test/language/nonlocal/assignment.wren
index 90fd6223..fb05caf6 100644
--- a/test/language/nonlocal/assignment.wren
+++ b/test/language/nonlocal/assignment.wren
@@ -1,7 +1,7 @@
 var Nonlocal = "before"
-IO.print(Nonlocal) // expect: before
+System.print(Nonlocal) // expect: before
 Nonlocal = "after"
-IO.print(Nonlocal) // expect: after
+System.print(Nonlocal) // expect: after
 
 class Foo {
   static method {
@@ -10,9 +10,9 @@ class Foo {
 }
 
 Foo.method
-IO.print(Nonlocal) // expect: method
+System.print(Nonlocal) // expect: method
 
 Fn.new {
   Nonlocal = "fn"
 }.call()
-IO.print(Nonlocal) // expect: fn
+System.print(Nonlocal) // expect: fn
diff --git a/test/language/nonlocal/in_block_scope.wren b/test/language/nonlocal/in_block_scope.wren
index 2c0ea96b..b8c3bbe3 100644
--- a/test/language/nonlocal/in_block_scope.wren
+++ b/test/language/nonlocal/in_block_scope.wren
@@ -2,7 +2,7 @@ var Nonlocal = "outer"
 
 {
   var Nonlocal = "inner"
-  IO.print(Nonlocal) // expect: inner
+  System.print(Nonlocal) // expect: inner
 }
 
-IO.print(Nonlocal) // expect: outer
+System.print(Nonlocal) // expect: outer
diff --git a/test/language/nonlocal/mutual_recursion.wren b/test/language/nonlocal/mutual_recursion.wren
index a0c9e65e..0eaf4948 100644
--- a/test/language/nonlocal/mutual_recursion.wren
+++ b/test/language/nonlocal/mutual_recursion.wren
@@ -8,5 +8,5 @@ class Bar {
   static foo { Foo.new() }
 }
 
-IO.print(Foo.bar) // expect: instance of Bar
-IO.print(Bar.foo) // expect: instance of Foo
+System.print(Foo.bar) // expect: instance of Bar
+System.print(Bar.foo) // expect: instance of Foo
diff --git a/test/language/nonlocal/nonlocal_in_initializer.wren b/test/language/nonlocal/nonlocal_in_initializer.wren
index 3faacdd8..6de6f473 100644
--- a/test/language/nonlocal/nonlocal_in_initializer.wren
+++ b/test/language/nonlocal/nonlocal_in_initializer.wren
@@ -1,2 +1,2 @@
 var A = A == null
-IO.print(A) // expect: true
+System.print(A) // expect: true
diff --git a/test/language/nonlocal/nonlocal_without_initializer.wren b/test/language/nonlocal/nonlocal_without_initializer.wren
index 2a08b8c9..5382e0d7 100644
--- a/test/language/nonlocal/nonlocal_without_initializer.wren
+++ b/test/language/nonlocal/nonlocal_without_initializer.wren
@@ -1,2 +1,2 @@
 var A
-IO.print(A) // expect: null
+System.print(A) // expect: null
diff --git a/test/language/nonlocal/null_before_defined.wren b/test/language/nonlocal/null_before_defined.wren
index f76f0536..5511db74 100644
--- a/test/language/nonlocal/null_before_defined.wren
+++ b/test/language/nonlocal/null_before_defined.wren
@@ -1,3 +1,3 @@
-IO.print(Foo) // expect: null
+System.print(Foo) // expect: null
 var Foo = "value"
-IO.print(Foo) // expect: value
+System.print(Foo) // expect: value
diff --git a/test/language/nonlocal/undefined.wren b/test/language/nonlocal/undefined.wren
index 7fab4f29..2ff78950 100644
--- a/test/language/nonlocal/undefined.wren
+++ b/test/language/nonlocal/undefined.wren
@@ -1,6 +1,6 @@
 var fn = Fn.new {
-  IO.print(Foo)
-  IO.print(Bar)
+  System.print(Foo)
+  System.print(Bar)
 }
 
 // expect error line 6
\ No newline at end of file
diff --git a/test/language/nonlocal/use_in_function.wren b/test/language/nonlocal/use_in_function.wren
index 657eeef2..cc1867cd 100644
--- a/test/language/nonlocal/use_in_function.wren
+++ b/test/language/nonlocal/use_in_function.wren
@@ -1,5 +1,5 @@
 var Global = "global"
 
 Fn.new {
-  IO.print(Global) // expect: global
+  System.print(Global) // expect: global
 }.call()
diff --git a/test/language/nonlocal/use_in_function_before_definition.wren b/test/language/nonlocal/use_in_function_before_definition.wren
index 1a797cc2..4c2934b3 100644
--- a/test/language/nonlocal/use_in_function_before_definition.wren
+++ b/test/language/nonlocal/use_in_function_before_definition.wren
@@ -1,5 +1,5 @@
 var f = Fn.new {
-  IO.print(Global)
+  System.print(Global)
 }
 
 var Global = "global"
diff --git a/test/language/nonlocal/use_in_method.wren b/test/language/nonlocal/use_in_method.wren
index 91945fa9..5d620e99 100644
--- a/test/language/nonlocal/use_in_method.wren
+++ b/test/language/nonlocal/use_in_method.wren
@@ -4,11 +4,11 @@ class Foo {
   construct new() {}
 
   method {
-    IO.print(Global)
+    System.print(Global)
   }
 
   static classMethod {
-    IO.print(Global)
+    System.print(Global)
   }
 }
 
diff --git a/test/language/nonlocal/use_in_method_before_definition.wren b/test/language/nonlocal/use_in_method_before_definition.wren
index 81f27b38..0498901b 100644
--- a/test/language/nonlocal/use_in_method_before_definition.wren
+++ b/test/language/nonlocal/use_in_method_before_definition.wren
@@ -2,11 +2,11 @@ class Foo {
   construct new() {}
 
   method {
-    IO.print(Global)
+    System.print(Global)
   }
 
   static classMethod {
-    IO.print(Global)
+    System.print(Global)
   }
 }
 
diff --git a/test/language/null/literal.wren b/test/language/null/literal.wren
index 8f59128c..b83dbc65 100644
--- a/test/language/null/literal.wren
+++ b/test/language/null/literal.wren
@@ -1 +1 @@
-IO.print(null) // expect: null
+System.print(null) // expect: null
diff --git a/test/language/number/hex_literals.wren b/test/language/number/hex_literals.wren
index 7a88fa5e..5a63d96d 100644
--- a/test/language/number/hex_literals.wren
+++ b/test/language/number/hex_literals.wren
@@ -1,8 +1,8 @@
 var x = 0xFF
 
-IO.print(x) // expect: 255
-IO.print(x + 1) // expect: 256
-IO.print(x == 255) // expect: true
-IO.print(0x09 is Num) // expect: true
-IO.print(x is Num) // expect: true
-IO.print(-0xFF) // expect: -255
\ No newline at end of file
+System.print(x) // expect: 255
+System.print(x + 1) // expect: 256
+System.print(x == 255) // expect: true
+System.print(0x09 is Num) // expect: true
+System.print(x is Num) // expect: true
+System.print(-0xFF) // expect: -255
\ No newline at end of file
diff --git a/test/language/number/literals.wren b/test/language/number/literals.wren
index 63f36e70..edf3f157 100644
--- a/test/language/number/literals.wren
+++ b/test/language/number/literals.wren
@@ -1,9 +1,9 @@
-IO.print(123)     // expect: 123
-IO.print(987654)  // expect: 987654
-IO.print(0)       // expect: 0
-IO.print(-0)      // expect: -0
+System.print(123)     // expect: 123
+System.print(987654)  // expect: 987654
+System.print(0)       // expect: 0
+System.print(-0)      // expect: -0
 
-IO.print(123.456) // expect: 123.456
-IO.print(-0.001)  // expect: -0.001
+System.print(123.456) // expect: 123.456
+System.print(-0.001)  // expect: -0.001
 
 // TODO: Literals at and beyond numeric limits.
diff --git a/test/language/number/scientific_literals.wren b/test/language/number/scientific_literals.wren
index 11024743..52695068 100644
--- a/test/language/number/scientific_literals.wren
+++ b/test/language/number/scientific_literals.wren
@@ -1,9 +1,9 @@
 var x = 2.55e2
 
-IO.print(x) // expect: 255
-IO.print(x + 1) // expect: 256
-IO.print(x == 255) // expect: true
-IO.print(2.55e-2 is Num) // expect: true
-IO.print(x is Num) // expect: true
-IO.print(-2.55e2) // expect: -255
-IO.print(-25500e-2) // expect: -255
+System.print(x) // expect: 255
+System.print(x + 1) // expect: 256
+System.print(x == 255) // expect: true
+System.print(2.55e-2 is Num) // expect: true
+System.print(x is Num) // expect: true
+System.print(-2.55e2) // expect: -255
+System.print(-25500e-2) // expect: -255
diff --git a/test/language/precedence.wren b/test/language/precedence.wren
index e14b110c..db9bbc1f 100644
--- a/test/language/precedence.wren
+++ b/test/language/precedence.wren
@@ -1,41 +1,41 @@
 // * has higher precedence than +.
-IO.print(2 + 3 * 4) // expect: 14
+System.print(2 + 3 * 4) // expect: 14
 
 // * has higher precedence than -.
-IO.print(20 - 3 * 4) // expect: 8
+System.print(20 - 3 * 4) // expect: 8
 
 // / has higher precedence than +.
-IO.print(2 + 6 / 3) // expect: 4
+System.print(2 + 6 / 3) // expect: 4
 
 // / has higher precedence than -.
-IO.print(2 - 6 / 3) // expect: 0
+System.print(2 - 6 / 3) // expect: 0
 
 // < has higher precedence than ==.
-IO.print(false == 2 < 1) // expect: true
+System.print(false == 2 < 1) // expect: true
 
 // > has higher precedence than ==.
-IO.print(false == 1 > 2) // expect: true
+System.print(false == 1 > 2) // expect: true
 
 // <= has higher precedence than ==.
-IO.print(false == 2 <= 1) // expect: true
+System.print(false == 2 <= 1) // expect: true
 
 // >= has higher precedence than ==.
-IO.print(false == 1 >= 2) // expect: true
+System.print(false == 1 >= 2) // expect: true
 
 // is has higher precedence than ==.
-IO.print(true == 10 is Num) // expect: true
-IO.print(10 is Num == false) // expect: false
+System.print(true == 10 is Num) // expect: true
+System.print(10 is Num == false) // expect: false
 
 // Unary - has lower precedence than ..
-IO.print(-"abc".count) // expect: -3
+System.print(-"abc".count) // expect: -3
 
 // 1 - 1 is not space-sensitive.
-IO.print(1 - 1) // expect: 0
-IO.print(1 -1)  // expect: 0
-IO.print(1- 1)  // expect: 0
-IO.print(1-1)   // expect: 0
+System.print(1 - 1) // expect: 0
+System.print(1 -1)  // expect: 0
+System.print(1- 1)  // expect: 0
+System.print(1-1)   // expect: 0
 
 // TODO: %, associativity.
 
 // Using () for grouping.
-IO.print((2 * (6 - (2 + 2)))) // expect: 4
+System.print((2 * (6 - (2 + 2)))) // expect: 4
diff --git a/test/language/return/after_else.wren b/test/language/return/after_else.wren
index 58ca87fe..f6c87559 100644
--- a/test/language/return/after_else.wren
+++ b/test/language/return/after_else.wren
@@ -1,3 +1,3 @@
-IO.print(Fn.new {
+System.print(Fn.new {
   if (false) "no" else return "ok"
 }.call()) // expect: ok
diff --git a/test/language/return/after_if.wren b/test/language/return/after_if.wren
index cd57363b..9d18c640 100644
--- a/test/language/return/after_if.wren
+++ b/test/language/return/after_if.wren
@@ -1,3 +1,3 @@
-IO.print(Fn.new {
+System.print(Fn.new {
   if (true) return "ok"
 }.call()) // expect: ok
diff --git a/test/language/return/after_while.wren b/test/language/return/after_while.wren
index 4f09fb3b..73800605 100644
--- a/test/language/return/after_while.wren
+++ b/test/language/return/after_while.wren
@@ -1,3 +1,3 @@
-IO.print(Fn.new {
+System.print(Fn.new {
   while (true) return "ok"
 }.call()) // expect: ok
diff --git a/test/language/return/in_function.wren b/test/language/return/in_function.wren
index 9b031b7e..42b6cfc0 100644
--- a/test/language/return/in_function.wren
+++ b/test/language/return/in_function.wren
@@ -1,6 +1,6 @@
 var f = Fn.new {
   return "ok"
-  IO.print("bad")
+  System.print("bad")
 }
 
-IO.print(f.call()) // expect: ok
+System.print(f.call()) // expect: ok
diff --git a/test/language/return/in_method.wren b/test/language/return/in_method.wren
index eeee1f38..485480d4 100644
--- a/test/language/return/in_method.wren
+++ b/test/language/return/in_method.wren
@@ -3,8 +3,8 @@ class Foo {
 
   method {
     return "ok"
-    IO.print("bad")
+    System.print("bad")
   }
 }
 
-IO.print(Foo.new().method) // expect: ok
+System.print(Foo.new().method) // expect: ok
diff --git a/test/language/return/return_null_if_newline.wren b/test/language/return/return_null_if_newline.wren
index d206dbe1..0afc88c3 100644
--- a/test/language/return/return_null_if_newline.wren
+++ b/test/language/return/return_null_if_newline.wren
@@ -1,6 +1,6 @@
 var f = Fn.new {
   return
-  IO.print("bad")
+  System.print("bad")
 }
 
-IO.print(f.call()) // expect: null
+System.print(f.call()) // expect: null
diff --git a/test/language/semicolon.wren b/test/language/semicolon.wren
index 7a5a8bfe..a7bd49f2 100644
--- a/test/language/semicolon.wren
+++ b/test/language/semicolon.wren
@@ -1,2 +1,2 @@
 // Semicolons are not valid separators.
-var a = "ok"; IO.print(a) // expect error
+var a = "ok"; System.print(a) // expect error
diff --git a/test/language/setter/associativity.wren b/test/language/setter/associativity.wren
index 4693502f..62cde71f 100644
--- a/test/language/setter/associativity.wren
+++ b/test/language/setter/associativity.wren
@@ -13,6 +13,6 @@ var c = Foo.new("c")
 
 // Assignment is right-associative.
 a.bar = b.bar = c.bar = "d"
-IO.print(a.toString) // expect: d
-IO.print(b.toString) // expect: d
-IO.print(c.toString) // expect: d
+System.print(a.toString) // expect: d
+System.print(b.toString) // expect: d
+System.print(c.toString) // expect: d
diff --git a/test/language/setter/instance.wren b/test/language/setter/instance.wren
index 05362131..b9688cca 100644
--- a/test/language/setter/instance.wren
+++ b/test/language/setter/instance.wren
@@ -2,7 +2,7 @@ class Foo {
   construct new() {}
 
   bar=(value) {
-    IO.print(value)
+    System.print(value)
   }
 }
 
diff --git a/test/language/setter/result.wren b/test/language/setter/result.wren
index dbc315c4..cd14d263 100644
--- a/test/language/setter/result.wren
+++ b/test/language/setter/result.wren
@@ -4,4 +4,4 @@ class Foo {
 }
 
 var foo = Foo.new()
-IO.print(foo.bar = "value") // expect: result
+System.print(foo.bar = "value") // expect: result
diff --git a/test/language/setter/same_name_as_method.wren b/test/language/setter/same_name_as_method.wren
index c6b34cc4..d4d7880d 100644
--- a/test/language/setter/same_name_as_method.wren
+++ b/test/language/setter/same_name_as_method.wren
@@ -1,7 +1,7 @@
 class Foo {
   construct new() {}
-  bar=(value) { IO.print("set") }
-  bar { IO.print("get") }
+  bar=(value) { System.print("set") }
+  bar { System.print("get") }
 }
 
 var foo = Foo.new()
diff --git a/test/language/setter/static.wren b/test/language/setter/static.wren
index e0c3850b..e3dcf875 100644
--- a/test/language/setter/static.wren
+++ b/test/language/setter/static.wren
@@ -1,6 +1,6 @@
 class Foo {
   static bar=(value) {
-    IO.print(value)
+    System.print(value)
   }
 }
 
diff --git a/test/language/shebang/shebang.wren b/test/language/shebang/shebang.wren
index 83f35c0a..e6bd8691 100644
--- a/test/language/shebang/shebang.wren
+++ b/test/language/shebang/shebang.wren
@@ -1,2 +1,2 @@
 #!/bin/wren
-IO.print("ok") // expect: ok
+System.print("ok") // expect: ok
diff --git a/test/language/shebang/shebang_at_other_line.wren b/test/language/shebang/shebang_at_other_line.wren
index 4fa3ac95..ee5234f8 100644
--- a/test/language/shebang/shebang_at_other_line.wren
+++ b/test/language/shebang/shebang_at_other_line.wren
@@ -1,3 +1,3 @@
 // expect error line 3
-IO.print("nope")
+System.print("nope")
 #!/bin/wren
\ No newline at end of file
diff --git a/test/language/shebang/shebang_invalid.wren b/test/language/shebang/shebang_invalid.wren
index 828c4fa0..3890ebe1 100644
--- a/test/language/shebang/shebang_invalid.wren
+++ b/test/language/shebang/shebang_invalid.wren
@@ -1,3 +1,3 @@
 #/invalid/shebang
 // expect error line 1
-IO.print("nope")
+System.print("nope")
diff --git a/test/language/static_field/closure.wren b/test/language/static_field/closure.wren
index 46e7d5b5..ecabd61e 100644
--- a/test/language/static_field/closure.wren
+++ b/test/language/static_field/closure.wren
@@ -11,6 +11,6 @@ class Foo {
 }
 
 Foo.initialize
-IO.print(Foo.closeOverGet.call()) // expect: Foo field
+System.print(Foo.closeOverGet.call()) // expect: Foo field
 Foo.closeOverSet.call()
-IO.print(Foo.closeOverGet.call()) // expect: new value
+System.print(Foo.closeOverGet.call()) // expect: new value
diff --git a/test/language/static_field/default_to_null.wren b/test/language/static_field/default_to_null.wren
index d5b06d2c..1832e7d3 100644
--- a/test/language/static_field/default_to_null.wren
+++ b/test/language/static_field/default_to_null.wren
@@ -1,5 +1,5 @@
 class Foo {
-  static write { IO.print(__field) }
+  static write { System.print(__field) }
 }
 
 Foo.write // expect: null
diff --git a/test/language/static_field/in_instance_method.wren b/test/language/static_field/in_instance_method.wren
index bb00412e..554dc59e 100644
--- a/test/language/static_field/in_instance_method.wren
+++ b/test/language/static_field/in_instance_method.wren
@@ -10,11 +10,11 @@ class Foo {
   }
 
   write() {
-    IO.print(__a)
-    IO.print(__b)
-    IO.print(__c)
-    IO.print(__d)
-    IO.print(__e)
+    System.print(__a)
+    System.print(__b)
+    System.print(__c)
+    System.print(__d)
+    System.print(__e)
   }
 }
 
diff --git a/test/language/static_field/multiple.wren b/test/language/static_field/multiple.wren
index f6b077b0..92934810 100644
--- a/test/language/static_field/multiple.wren
+++ b/test/language/static_field/multiple.wren
@@ -8,11 +8,11 @@ class Foo {
   }
 
   static write {
-    IO.print(__a)
-    IO.print(__b)
-    IO.print(__c)
-    IO.print(__d)
-    IO.print(__e)
+    System.print(__a)
+    System.print(__b)
+    System.print(__c)
+    System.print(__d)
+    System.print(__e)
   }
 }
 
diff --git a/test/language/static_field/nested_class.wren b/test/language/static_field/nested_class.wren
index 8e1ce892..df1c6d3d 100644
--- a/test/language/static_field/nested_class.wren
+++ b/test/language/static_field/nested_class.wren
@@ -3,36 +3,36 @@ class Outer {
 
   static staticMethod {
     __field = "outer"
-    IO.print(__field) // expect: outer
+    System.print(__field) // expect: outer
 
     class Inner {
       construct new() {}
 
       static staticMethod {
         __field = "inner"
-        IO.print(__field) // expect: inner
+        System.print(__field) // expect: inner
       }
     }
 
     Inner.staticMethod
-    IO.print(__field) // expect: outer
+    System.print(__field) // expect: outer
   }
 
   instanceMethod {
     __field = "outer"
-    IO.print(__field) // expect: outer
+    System.print(__field) // expect: outer
 
     class Inner {
       construct new() {}
 
       instanceMethod {
         __field = "inner"
-        IO.print(__field) // expect: inner
+        System.print(__field) // expect: inner
       }
     }
 
     Inner.new().instanceMethod
-    IO.print(__field) // expect: outer
+    System.print(__field) // expect: outer
   }
 }
 
diff --git a/test/language/static_field/use_before_set.wren b/test/language/static_field/use_before_set.wren
index 1daeaa89..d2cfa1fc 100644
--- a/test/language/static_field/use_before_set.wren
+++ b/test/language/static_field/use_before_set.wren
@@ -1,5 +1,5 @@
 class Foo {
-  static write { IO.print(__field) } // Compile a use of the field...
+  static write { System.print(__field) } // Compile a use of the field...
   static init { __field = "value" }  // ...before an assignment to it.
 }
 
diff --git a/test/language/string/byte_escapes.wren b/test/language/string/byte_escapes.wren
index 9d29d148..0d26e699 100644
--- a/test/language/string/byte_escapes.wren
+++ b/test/language/string/byte_escapes.wren
@@ -1,12 +1,12 @@
 var bytes = "\x00\x12\x34\x56\x78\xab\xCD\xfFf".bytes
 
-IO.print(bytes[0]) // expect: 0
-IO.print(bytes[1]) // expect: 18
-IO.print(bytes[2]) // expect: 52
-IO.print(bytes[3]) // expect: 86
-IO.print(bytes[4]) // expect: 120
-IO.print(bytes[5]) // expect: 171
-IO.print(bytes[6]) // expect: 205
-IO.print(bytes[7]) // expect: 255
+System.print(bytes[0]) // expect: 0
+System.print(bytes[1]) // expect: 18
+System.print(bytes[2]) // expect: 52
+System.print(bytes[3]) // expect: 86
+System.print(bytes[4]) // expect: 120
+System.print(bytes[5]) // expect: 171
+System.print(bytes[6]) // expect: 205
+System.print(bytes[7]) // expect: 255
 // "f".
-IO.print(bytes[8]) // expect: 102
+System.print(bytes[8]) // expect: 102
diff --git a/test/language/string/escapes.wren b/test/language/string/escapes.wren
index eaf5ab75..70628b45 100644
--- a/test/language/string/escapes.wren
+++ b/test/language/string/escapes.wren
@@ -1,7 +1,7 @@
 // Escape characters.
-IO.print("\"")     // expect: "
-IO.print("\\")     // expect: \
-IO.print("(\n)")   // expect: (
+System.print("\"")     // expect: "
+System.print("\\")     // expect: \
+System.print("(\n)")   // expect: (
                    // expect: )
 
 // TODO: Non-printing escapes like \t.
diff --git a/test/language/string/literals.wren b/test/language/string/literals.wren
index 870d3f89..a51124f9 100644
--- a/test/language/string/literals.wren
+++ b/test/language/string/literals.wren
@@ -1,5 +1,5 @@
-IO.print("".count)   // expect: 0
-IO.print("a string") // expect: a string
+System.print("".count)   // expect: 0
+System.print("a string") // expect: a string
 
 // Non-ASCII.
-IO.print("A~¶Þॐஃ") // expect: A~¶Þॐஃ
+System.print("A~¶Þॐஃ") // expect: A~¶Þॐஃ
diff --git a/test/language/string/unicode_escapes.wren b/test/language/string/unicode_escapes.wren
index e15c4447..786cefe4 100644
--- a/test/language/string/unicode_escapes.wren
+++ b/test/language/string/unicode_escapes.wren
@@ -1,17 +1,17 @@
 // One byte UTF-8 Sequences.
-IO.print("\u0041")     // expect: A
-IO.print("\u007e")     // expect: ~
+System.print("\u0041")     // expect: A
+System.print("\u007e")     // expect: ~
 
 // Two byte sequences.
-IO.print("\u00b6")     // expect: ¶
-IO.print("\u00de")     // expect: Þ
+System.print("\u00b6")     // expect: ¶
+System.print("\u00de")     // expect: Þ
 
 // Three byte sequences.
-IO.print("\u0950")     // expect: ॐ
-IO.print("\u0b83")     // expect: ஃ
+System.print("\u0950")     // expect: ॐ
+System.print("\u0b83")     // expect: ஃ
 
 // Capitalized hex.
-IO.print("\u00B6")     // expect: ¶
-IO.print("\u00DE")     // expect: Þ
+System.print("\u00B6")     // expect: ¶
+System.print("\u00DE")     // expect: Þ
 
 // TODO: Syntax for Unicode escapes > 0xffff?
diff --git a/test/language/super/call_different_arity.wren b/test/language/super/call_different_arity.wren
index 03edb94f..58fb8ab7 100644
--- a/test/language/super/call_different_arity.wren
+++ b/test/language/super/call_different_arity.wren
@@ -1,14 +1,14 @@
 class Base {
-  foo { IO.print("Base.foo") }
-  foo(a) { IO.print("Base.foo(a)") }
-  foo(a, b) { IO.print("Base.foo(a, b)") }
+  foo { System.print("Base.foo") }
+  foo(a) { System.print("Base.foo(a)") }
+  foo(a, b) { System.print("Base.foo(a, b)") }
 }
 
 class Derived is Base {
   construct new() {}
 
   foo(a) {
-    IO.print("Derived.bar(a)")
+    System.print("Derived.bar(a)")
     super
     super(1)
     super(1, 2)
diff --git a/test/language/super/call_other_method.wren b/test/language/super/call_other_method.wren
index e048ac5b..35a6d512 100644
--- a/test/language/super/call_other_method.wren
+++ b/test/language/super/call_other_method.wren
@@ -1,6 +1,6 @@
 class Base {
   foo {
-    IO.print("Base.foo")
+    System.print("Base.foo")
   }
 }
 
@@ -8,7 +8,7 @@ class Derived is Base {
   construct new() {}
 
   bar {
-    IO.print("Derived.bar")
+    System.print("Derived.bar")
     super.foo
   }
 }
diff --git a/test/language/super/call_same_method.wren b/test/language/super/call_same_method.wren
index a70d60bf..07a08c57 100644
--- a/test/language/super/call_same_method.wren
+++ b/test/language/super/call_same_method.wren
@@ -1,6 +1,6 @@
 class Base {
   foo {
-    IO.print("Base.foo")
+    System.print("Base.foo")
   }
 }
 
@@ -8,7 +8,7 @@ class Derived is Base {
   construct new() {}
 
   foo {
-    IO.print("Derived.foo")
+    System.print("Derived.foo")
     super.foo
   }
 }
diff --git a/test/language/super/closure.wren b/test/language/super/closure.wren
index b1302467..83b53df4 100644
--- a/test/language/super/closure.wren
+++ b/test/language/super/closure.wren
@@ -9,4 +9,4 @@ class Derived is Base {
 }
 
 var closure = Derived.new().getClosure
-IO.print(closure.call()) // expect: Base
+System.print(closure.call()) // expect: Base
diff --git a/test/language/super/implicit_name.wren b/test/language/super/implicit_name.wren
index 75100560..ee73ff1e 100644
--- a/test/language/super/implicit_name.wren
+++ b/test/language/super/implicit_name.wren
@@ -1,6 +1,6 @@
 class Base {
   foo {
-    IO.print("Base.foo")
+    System.print("Base.foo")
   }
 }
 
@@ -8,7 +8,7 @@ class Derived is Base {
   construct new() {}
 
   foo {
-    IO.print("Derived.foo")
+    System.print("Derived.foo")
     super
   }
 }
diff --git a/test/language/super/indirectly_inherited.wren b/test/language/super/indirectly_inherited.wren
index 765459b8..a754fdf5 100644
--- a/test/language/super/indirectly_inherited.wren
+++ b/test/language/super/indirectly_inherited.wren
@@ -1,6 +1,6 @@
 class A {
   foo {
-    IO.print("A.foo")
+    System.print("A.foo")
   }
 }
 
@@ -10,7 +10,7 @@ class C is B {
   construct new() {}
 
   foo {
-    IO.print("C.foo")
+    System.print("C.foo")
     super.foo
   }
 }
diff --git a/test/language/super/super_in_closure_in_inherited_method.wren b/test/language/super/super_in_closure_in_inherited_method.wren
index ef97d602..de712455 100644
--- a/test/language/super/super_in_closure_in_inherited_method.wren
+++ b/test/language/super/super_in_closure_in_inherited_method.wren
@@ -10,4 +10,4 @@ class B is A {
   construct new() {}
 }
 
-IO.print(B.new().callSuperToString) // expect: instance of B
+System.print(B.new().callSuperToString) // expect: instance of B
diff --git a/test/language/super/super_in_inherited_method.wren b/test/language/super/super_in_inherited_method.wren
index 1a7e914d..cab2f762 100644
--- a/test/language/super/super_in_inherited_method.wren
+++ b/test/language/super/super_in_inherited_method.wren
@@ -8,4 +8,4 @@ class B is A {
   construct new() {}
 }
 
-IO.print(B.new().callSuperToString) // expect: instance of B
+System.print(B.new().callSuperToString) // expect: instance of B
diff --git a/test/language/this/closure.wren b/test/language/this/closure.wren
index d254b371..60d49a58 100644
--- a/test/language/this/closure.wren
+++ b/test/language/this/closure.wren
@@ -5,4 +5,4 @@ class Foo {
 }
 
 var closure = Foo.new().getClosure
-IO.print(closure.call()) // expect: Foo
+System.print(closure.call()) // expect: Foo
diff --git a/test/language/this/nested_class.wren b/test/language/this/nested_class.wren
index f7c5351f..3b207422 100644
--- a/test/language/this/nested_class.wren
+++ b/test/language/this/nested_class.wren
@@ -2,16 +2,16 @@ class Outer {
   construct new() {}
 
   method {
-    IO.print(this) // expect: Outer
+    System.print(this) // expect: Outer
 
     Fn.new {
-      IO.print(this) // expect: Outer
+      System.print(this) // expect: Outer
 
       class Inner {
         construct new() {}
 
         method {
-          IO.print(this) // expect: Inner
+          System.print(this) // expect: Inner
         }
         toString { "Inner" }
       }
diff --git a/test/language/this/nested_closure.wren b/test/language/this/nested_closure.wren
index ccb5f146..6c36d09d 100644
--- a/test/language/this/nested_closure.wren
+++ b/test/language/this/nested_closure.wren
@@ -5,4 +5,4 @@ class Foo {
 }
 
 var closure = Foo.new().getClosure
-IO.print(closure.call().call().call()) // expect: Foo
+System.print(closure.call().call().call()) // expect: Foo
diff --git a/test/language/this/this_in_method.wren b/test/language/this/this_in_method.wren
index ba212a56..08e31b4d 100644
--- a/test/language/this/this_in_method.wren
+++ b/test/language/this/this_in_method.wren
@@ -4,4 +4,4 @@ class Foo {
   baz { "baz" }
 }
 
-IO.print(Foo.new().bar.baz) // expect: baz
+System.print(Foo.new().bar.baz) // expect: baz
diff --git a/test/language/this/this_in_static_method.wren b/test/language/this/this_in_static_method.wren
index 9d07b71a..5a89057f 100644
--- a/test/language/this/this_in_static_method.wren
+++ b/test/language/this/this_in_static_method.wren
@@ -1,7 +1,7 @@
 class Foo {
   static test {
-    IO.print(this == Foo) // expect: true
-    IO.print(this.bar) // expect: bar
+    System.print(this == Foo) // expect: true
+    System.print(this.bar) // expect: bar
   }
 
   static bar { "bar" }
diff --git a/test/language/unexpected_character.wren b/test/language/unexpected_character.wren
index 49b486c2..22a81a17 100644
--- a/test/language/unexpected_character.wren
+++ b/test/language/unexpected_character.wren
@@ -1,3 +1,3 @@
-IO.print("no")
+System.print("no")
 // Something that's not a valid character:
 ^ // expect error
diff --git a/test/language/variable/global_without_initializer.wren b/test/language/variable/global_without_initializer.wren
index e934ae7e..bd1c043d 100644
--- a/test/language/variable/global_without_initializer.wren
+++ b/test/language/variable/global_without_initializer.wren
@@ -1,2 +1,2 @@
 var a
-IO.print(a) // expect: null
+System.print(a) // expect: null
diff --git a/test/language/variable/local_in_initializer.wren b/test/language/variable/local_in_initializer.wren
index 9cffc4c0..5d397e46 100644
--- a/test/language/variable/local_in_initializer.wren
+++ b/test/language/variable/local_in_initializer.wren
@@ -1,4 +1,4 @@
 {
   var a = a + 1 // expect error
-  IO.print(a)
+  System.print(a)
 }
diff --git a/test/language/variable/local_in_middle_of_block.wren b/test/language/variable/local_in_middle_of_block.wren
index 47266af1..3768329c 100644
--- a/test/language/variable/local_in_middle_of_block.wren
+++ b/test/language/variable/local_in_middle_of_block.wren
@@ -3,13 +3,13 @@ class Foo {
 
   bar {
     var a = "a"
-    IO.print(a) // expect: a
+    System.print(a) // expect: a
     var b = a + " b"
-    IO.print(b) // expect: a b
+    System.print(b) // expect: a b
     var c = a + " c"
-    IO.print(c) // expect: a c
+    System.print(c) // expect: a c
     var d = b + " d"
-    IO.print(d) // expect: a b d
+    System.print(d) // expect: a b d
   }
 }
 
diff --git a/test/language/variable/local_in_nested_block.wren b/test/language/variable/local_in_nested_block.wren
index 11a82485..e4174410 100644
--- a/test/language/variable/local_in_nested_block.wren
+++ b/test/language/variable/local_in_nested_block.wren
@@ -1,6 +1,6 @@
 {
   var a = "outer"
   {
-    IO.print(a) // expect: outer
+    System.print(a) // expect: outer
   }
 }
\ No newline at end of file
diff --git a/test/language/variable/local_without_initializer.wren b/test/language/variable/local_without_initializer.wren
index 2daea492..f96e96c8 100644
--- a/test/language/variable/local_without_initializer.wren
+++ b/test/language/variable/local_without_initializer.wren
@@ -1,4 +1,4 @@
 {
   var a
-  IO.print(a) // expect: null
+  System.print(a) // expect: null
 }
diff --git a/test/language/variable/many_locals.wren b/test/language/variable/many_locals.wren
index d8ab0a5d..97cc20c7 100644
--- a/test/language/variable/many_locals.wren
+++ b/test/language/variable/many_locals.wren
@@ -255,5 +255,5 @@
   var a253 = a252
   var a254 = a253
   var a255 = a254
-  IO.print(a255) // expect: value
+  System.print(a255) // expect: value
 }
diff --git a/test/language/variable/many_nonsimultaneous_locals.wren b/test/language/variable/many_nonsimultaneous_locals.wren
index 2d81fd37..8320c1e9 100644
--- a/test/language/variable/many_nonsimultaneous_locals.wren
+++ b/test/language/variable/many_nonsimultaneous_locals.wren
@@ -259,7 +259,7 @@
     var a253 = a252
     var a254 = a253
     var a255 = a254
-    IO.print(a255) // expect: value a
+    System.print(a255) // expect: value a
   }
 
   {
@@ -519,6 +519,6 @@
     var b253 = b252
     var b254 = b253
     var b255 = b254
-    IO.print(b255) // expect: value b
+    System.print(b255) // expect: value b
   }
 }
diff --git a/test/language/variable/outside_method.wren b/test/language/variable/outside_method.wren
index b2a5d59d..1430b56f 100644
--- a/test/language/variable/outside_method.wren
+++ b/test/language/variable/outside_method.wren
@@ -6,13 +6,13 @@ class Foo {
   foo { "method" }
 
   method {
-    IO.print(foo)
+    System.print(foo)
   }
 
   static foo { "class method" }
 
   static classMethod {
-    IO.print(foo)
+    System.print(foo)
   }
 }
 
diff --git a/test/language/variable/scope_if.wren b/test/language/variable/scope_if.wren
index 6fc8a225..9c965b26 100644
--- a/test/language/variable/scope_if.wren
+++ b/test/language/variable/scope_if.wren
@@ -3,11 +3,11 @@ var a = "out"
 if (true) {
   var a = "in"
 }
-IO.print(a) // expect: out
+System.print(a) // expect: out
 
 // Create a local scope for the 'else' expression.
 var b = "out"
 if (false) "dummy" else {
   var b = "in"
 }
-IO.print(b) // expect: out
+System.print(b) // expect: out
diff --git a/test/language/variable/scope_reuse_in_different_blocks.wren b/test/language/variable/scope_reuse_in_different_blocks.wren
index 92796bab..e452cb4d 100644
--- a/test/language/variable/scope_reuse_in_different_blocks.wren
+++ b/test/language/variable/scope_reuse_in_different_blocks.wren
@@ -1,9 +1,9 @@
 {
   var a = "first"
-  IO.print(a) // expect: first
+  System.print(a) // expect: first
 }
 
 {
   var a = "second"
-  IO.print(a) // expect: second
+  System.print(a) // expect: second
 }
diff --git a/test/language/variable/scope_while.wren b/test/language/variable/scope_while.wren
index d8e215b5..a6fe29c3 100644
--- a/test/language/variable/scope_while.wren
+++ b/test/language/variable/scope_while.wren
@@ -4,4 +4,4 @@ var i = 0
 while ((i = i + 1) <= 1) {
   var a = "inner"
 }
-IO.print(a) // expect: outer
+System.print(a) // expect: outer
diff --git a/test/language/variable/shadow_and_local.wren b/test/language/variable/shadow_and_local.wren
index e069a0bf..500fe2ab 100644
--- a/test/language/variable/shadow_and_local.wren
+++ b/test/language/variable/shadow_and_local.wren
@@ -1,8 +1,8 @@
 {
   var a = "outer"
   {
-    IO.print(a) // expect: outer
+    System.print(a) // expect: outer
     var a = "inner"
-    IO.print(a) // expect: inner
+    System.print(a) // expect: inner
   }
 }
\ No newline at end of file
diff --git a/test/language/variable/shadow_global.wren b/test/language/variable/shadow_global.wren
index 8f86f37d..6d62e55b 100644
--- a/test/language/variable/shadow_global.wren
+++ b/test/language/variable/shadow_global.wren
@@ -1,6 +1,6 @@
 var a = "global"
 {
   var a = "shadow"
-  IO.print(a) // expect: shadow
+  System.print(a) // expect: shadow
 }
-IO.print(a) // expect: global
\ No newline at end of file
+System.print(a) // expect: global
\ No newline at end of file
diff --git a/test/language/variable/shadow_in_initializer.wren b/test/language/variable/shadow_in_initializer.wren
index e0f76a4c..d6055b7a 100644
--- a/test/language/variable/shadow_in_initializer.wren
+++ b/test/language/variable/shadow_in_initializer.wren
@@ -2,6 +2,6 @@
   var a = "outer"
   {
     var a = a + " inner"
-    IO.print(a) // expect: outer inner
+    System.print(a) // expect: outer inner
   }
 }
diff --git a/test/language/variable/shadow_local.wren b/test/language/variable/shadow_local.wren
index 8234a5c4..0c913b14 100644
--- a/test/language/variable/shadow_local.wren
+++ b/test/language/variable/shadow_local.wren
@@ -2,7 +2,7 @@
   var a = "local"
   {
     var a = "shadow"
-    IO.print(a) // expect: shadow
+    System.print(a) // expect: shadow
   }
-  IO.print(a) // expect: local
+  System.print(a) // expect: local
 }
\ No newline at end of file
diff --git a/test/language/variable/undefined_global.wren b/test/language/variable/undefined_global.wren
index 196b010b..f470fe6a 100644
--- a/test/language/variable/undefined_global.wren
+++ b/test/language/variable/undefined_global.wren
@@ -1 +1 @@
-IO.print(notDefined)  // expect error
+System.print(notDefined)  // expect error
diff --git a/test/language/variable/undefined_local.wren b/test/language/variable/undefined_local.wren
index a9592bef..da8f1098 100644
--- a/test/language/variable/undefined_local.wren
+++ b/test/language/variable/undefined_local.wren
@@ -1,3 +1,3 @@
 Fn.new {
-  IO.print(notDefined)  // expect error
+  System.print(notDefined)  // expect error
 }.call()
diff --git a/test/language/while/closure_in_body.wren b/test/language/while/closure_in_body.wren
index adc0cf57..41134424 100644
--- a/test/language/while/closure_in_body.wren
+++ b/test/language/while/closure_in_body.wren
@@ -3,7 +3,7 @@ var list = []
 var i = 1
 while (i < 4) {
   var j = i + 1
-  list.add(Fn.new { IO.print(j) })
+  list.add(Fn.new { System.print(j) })
   i = i + 1
 }
 
diff --git a/test/language/while/newline_after_while.wren b/test/language/while/newline_after_while.wren
index 7bc26cc0..282d9938 100644
--- a/test/language/while/newline_after_while.wren
+++ b/test/language/while/newline_after_while.wren
@@ -1,2 +1,2 @@
 while // expect error
-(true) IO.print("bad")
+(true) System.print("bad")
diff --git a/test/language/while/return_closure.wren b/test/language/while/return_closure.wren
index 89859339..628f363e 100644
--- a/test/language/while/return_closure.wren
+++ b/test/language/while/return_closure.wren
@@ -1,7 +1,7 @@
 var f = Fn.new {
   while (true) {
     var i = "i"
-    return Fn.new { IO.print(i) }
+    return Fn.new { System.print(i) }
   }
 }
 
diff --git a/test/language/while/return_inside.wren b/test/language/while/return_inside.wren
index 33ec8887..ab7dcde0 100644
--- a/test/language/while/return_inside.wren
+++ b/test/language/while/return_inside.wren
@@ -5,5 +5,5 @@ var f = Fn.new {
   }
 }
 
-IO.print(f.call())
+System.print(f.call())
 // expect: i
diff --git a/test/language/while/syntax.wren b/test/language/while/syntax.wren
index 5398dd8e..6244aa81 100644
--- a/test/language/while/syntax.wren
+++ b/test/language/while/syntax.wren
@@ -1,6 +1,6 @@
 // Single-expression body.
 var c = 0
-while (c < 3) IO.print(c = c + 1)
+while (c < 3) System.print(c = c + 1)
 // expect: 1
 // expect: 2
 // expect: 3
@@ -8,7 +8,7 @@ while (c < 3) IO.print(c = c + 1)
 // Block body.
 var a = 0
 while (a < 3) {
-  IO.print(a)
+  System.print(a)
   a = a + 1
 }
 // expect: 0
diff --git a/test/language/while/truth.wren b/test/language/while/truth.wren
index 32a625b2..ece02e7f 100644
--- a/test/language/while/truth.wren
+++ b/test/language/while/truth.wren
@@ -1,26 +1,26 @@
 // False and null are false.
 while (false) {
-  IO.print("bad")
+  System.print("bad")
   break
 }
 
 while (null) {
-  IO.print("bad")
+  System.print("bad")
   break
 }
 
 // Everything else is true.
 while (true) {
-  IO.print("true") // expect: true
+  System.print("true") // expect: true
   break
 }
 
 while (0) {
-  IO.print(0) // expect: 0
+  System.print(0) // expect: 0
   break
 }
 
 while ("") {
-  IO.print("string") // expect: string
+  System.print("string") // expect: string
   break
 }
diff --git a/test/language/whitespace.wren b/test/language/whitespace.wren
index a5fac6b2..3ff2a9c3 100644
--- a/test/language/whitespace.wren
+++ b/test/language/whitespace.wren
@@ -1,26 +1,26 @@
 // No indent
-IO.print("ok") // expect: ok
+System.print("ok") // expect: ok
 
 // Indent with space
-  IO.print("ok") // expect: ok
+  System.print("ok") // expect: ok
 
 // Indent with tab
-	IO.print("ok") // expect: ok
+	System.print("ok") // expect: ok
 
 // Indent with space then tab
-  	IO.print("ok") // expect: ok
+  	System.print("ok") // expect: ok
 
 // Indent with tab then space
-	  IO.print("ok") // expect: ok
+	  System.print("ok") // expect: ok
 
 // Indent with mixed tab and space
-  	  	IO.print("ok") // expect: ok
+  	  	System.print("ok") // expect: ok
 
 // Space in with code
-IO . print ( "ok" ) // expect: ok
+System . print ( "ok" ) // expect: ok
 
 // Tab in with code
-IO	.	print	(	"ok"	) // expect: ok
+System	.	print	(	"ok"	) // expect: ok
 
 // Tab and space mixed in with code
-IO	 . 	print 	(	 "ok" 	) // expect: ok
+System	 . 	print 	(	 "ok" 	) // expect: ok
diff --git a/test/limit/long_function.wren b/test/limit/long_function.wren
index 61e97836..255dae38 100644
--- a/test/limit/long_function.wren
+++ b/test/limit/long_function.wren
@@ -1,1013 +1,1013 @@
 Fn.new {
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
   // 100
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
   // 200
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
   // 300
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
   // 400
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
   // 500
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
   // 600
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
   // 700
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
   // 800
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
   // 900
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
-  IO.print(1) // expect: 1
-  IO.print(2) // expect: 2
-  IO.print(3) // expect: 3
-  IO.print(4) // expect: 4
-  IO.print(5) // expect: 5
-  IO.print(6) // expect: 6
-  IO.print(7) // expect: 7
-  IO.print(8) // expect: 8
-  IO.print(9) // expect: 9
-  IO.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
+  System.print(1) // expect: 1
+  System.print(2) // expect: 2
+  System.print(3) // expect: 3
+  System.print(4) // expect: 4
+  System.print(5) // expect: 5
+  System.print(6) // expect: 6
+  System.print(7) // expect: 7
+  System.print(8) // expect: 8
+  System.print(9) // expect: 9
+  System.print(10) // expect: 10
   // 1000
 }.call()
 
diff --git a/test/limit/long_string.wren b/test/limit/long_string.wren
index eeb7724d..cdde68f1 100644
--- a/test/limit/long_string.wren
+++ b/test/limit/long_string.wren
@@ -1,6 +1,6 @@
 // Create a very long string containing escape sequences.
 var s = "1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\n1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\n1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\n1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\n1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\n1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\n1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\n1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\n1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\n1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890\"1234567890"
-IO.print(s)
+System.print(s)
 // expect: 1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890
 // expect: 1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890
 // expect: 1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890"1234567890
diff --git a/test/limit/many_constants.wren b/test/limit/many_constants.wren
index 6328799c..678cdf6c 100644
--- a/test/limit/many_constants.wren
+++ b/test/limit/many_constants.wren
@@ -65534,7 +65534,7 @@ var f = Fn.new {
   65533
   65534
   65535
-  IO.print(65536)
+  System.print(65536)
 }
 
 f.call() // expect: 65536
diff --git a/test/limit/many_fields.wren b/test/limit/many_fields.wren
index eed2a9b6..15d469ce 100644
--- a/test/limit/many_fields.wren
+++ b/test/limit/many_fields.wren
@@ -255,7 +255,7 @@ class Foo {
     _field253 = 253
     _field254 = 254
     _field255 = 255
-    IO.print(_field255)
+    System.print(_field255)
   }
 }
 
diff --git a/test/limit/many_globals.wren b/test/limit/many_globals.wren
index a237f52c..65710d5e 100644
--- a/test/limit/many_globals.wren
+++ b/test/limit/many_globals.wren
@@ -4095,7 +4095,7 @@ var global4094 = 4094
 var global4095 = 4095
 var global4096 = 4096
 
-IO.print(global4096) // expect: 4096
+System.print(global4096) // expect: 4096
 
 // Symbol tables currently use O(n) to look up names. This makes this test
 // painfully slow when a large number of names are defined. This is a
@@ -65484,5 +65484,5 @@ var global65472 = 65472
 // Not defining the full 65,536 here because the core library also defines some
 // global names.
 
-IO.print(global65472) // expect 65472
+System.print(global65472) // expect 65472
 */
diff --git a/test/limit/many_inherited_fields.wren b/test/limit/many_inherited_fields.wren
index c63e99b1..4baea699 100644
--- a/test/limit/many_inherited_fields.wren
+++ b/test/limit/many_inherited_fields.wren
@@ -131,8 +131,8 @@ class Foo {
   }
 
   foo {
-    IO.print(_field1)
-    IO.print(_field128)
+    System.print(_field1)
+    System.print(_field128)
   }
 }
 
@@ -269,8 +269,8 @@ class Bar is Foo {
   }
 
   bar {
-    IO.print(_field129)
-    IO.print(_field255)
+    System.print(_field129)
+    System.print(_field255)
   }
 }
 
diff --git a/test/limit/too_many_constants.wren b/test/limit/too_many_constants.wren
index 9bdf97f5..48ea226a 100644
--- a/test/limit/too_many_constants.wren
+++ b/test/limit/too_many_constants.wren
@@ -65535,5 +65535,5 @@ var f = Fn.new {
   65534
   65535
   66536
-  IO.print(65537) // expect error
+  System.print(65537) // expect error
 }
diff --git a/test/limit/too_many_inherited_fields.wren b/test/limit/too_many_inherited_fields.wren
index 0c90bff1..f95f679f 100644
--- a/test/limit/too_many_inherited_fields.wren
+++ b/test/limit/too_many_inherited_fields.wren
@@ -131,8 +131,8 @@ class Foo {
   }
 
   foo {
-    IO.print(_field1)
-    IO.print(_field128)
+    System.print(_field1)
+    System.print(_field128)
   }
 }
 
@@ -270,8 +270,8 @@ class Bar is Foo { // expect runtime error: Class 'Bar' may not have more than 2
   }
 
   bar {
-    IO.print(_field129)
-    IO.print(_field256)
+    System.print(_field129)
+    System.print(_field256)
   }
 }
 
diff --git a/test/meta/eval_existing_scoped_variable.wren b/test/meta/eval_existing_scoped_variable.wren
index 90c44873..82b80466 100644
--- a/test/meta/eval_existing_scoped_variable.wren
+++ b/test/meta/eval_existing_scoped_variable.wren
@@ -2,4 +2,4 @@ var y
 
 Meta.eval("y = 2")
 
-IO.print(y) // expect: 2
\ No newline at end of file
+System.print(y) // expect: 2
\ No newline at end of file
diff --git a/test/scheduler/add.wren b/test/scheduler/add.wren
index 7dd7d08e..e12062bc 100644
--- a/test/scheduler/add.wren
+++ b/test/scheduler/add.wren
@@ -7,9 +7,9 @@ Scheduler.add {
 }
 
 // Does not run immediately.
-IO.print(run) // expect: false
+System.print(run) // expect: false
 
 Timer.sleep(0)
 
 // Runs when the main fiber suspends on IO.
-IO.print(run) // expect: true
+System.print(run) // expect: true
diff --git a/test/timer/sleep_called_fibers.wren b/test/timer/sleep_called_fibers.wren
index a5598ef0..bb77cb49 100644
--- a/test/timer/sleep_called_fibers.wren
+++ b/test/timer/sleep_called_fibers.wren
@@ -1,21 +1,21 @@
 import "timer" for Timer
 
 var a = Fiber.new {
-  IO.print("a before")
+  System.print("a before")
   Timer.sleep(10)
-  IO.print("a after")
+  System.print("a after")
 }
 
 var b = Fiber.new {
-  IO.print("b before")
+  System.print("b before")
   a.call()
-  IO.print("b after")
+  System.print("b after")
 }
 
 // All fibers are suspended since they were directly called and not scheduled.
-IO.print("before")  // expect: before
+System.print("before")  // expect: before
 b.call()            // expect: b before
                     // expect: a before
                     // expect: a after
                     // expect: b after
-IO.print("done")    // expect: done
+System.print("done")    // expect: done
diff --git a/test/timer/sleep_fibers.wren b/test/timer/sleep_fibers.wren
index e7038234..68706de0 100644
--- a/test/timer/sleep_fibers.wren
+++ b/test/timer/sleep_fibers.wren
@@ -3,17 +3,17 @@ import "timer" for Timer
 
 Scheduler.add {
   Timer.sleep(2)
-  IO.print("a")
+  System.print("a")
 }
 
 Scheduler.add {
   Timer.sleep(1)
-  IO.print("b")
+  System.print("b")
 }
 
-IO.print("main")
+System.print("main")
 Timer.sleep(3)
-IO.print("done")
+System.print("done")
 // expect: main
 // expect: b
 // expect: a
diff --git a/test/timer/sleep_float.wren b/test/timer/sleep_float.wren
index 43142986..b166ab30 100644
--- a/test/timer/sleep_float.wren
+++ b/test/timer/sleep_float.wren
@@ -4,17 +4,17 @@ import "timer" for Timer
 // These are both rounded to 1, so "a" should complete first.
 Scheduler.add {
   Timer.sleep(1.5)
-  IO.print("a")
+  System.print("a")
 }
 
 Scheduler.add {
   Timer.sleep(1.3)
-  IO.print("b")
+  System.print("b")
 }
 
-IO.print("main")
+System.print("main")
 Timer.sleep(3)
-IO.print("done")
+System.print("done")
 // expect: main
 // expect: a
 // expect: b
diff --git a/test/timer/sleep_main_fiber.wren b/test/timer/sleep_main_fiber.wren
index 3e3e43fb..302d6917 100644
--- a/test/timer/sleep_main_fiber.wren
+++ b/test/timer/sleep_main_fiber.wren
@@ -1,9 +1,9 @@
 import "timer" for Timer
 
-IO.print("1") // expect: 1
+System.print("1") // expect: 1
 Timer.sleep(3)
-IO.print("2") // expect: 2
+System.print("2") // expect: 2
 Timer.sleep(3)
-IO.print("3") // expect: 3
+System.print("3") // expect: 3
 Timer.sleep(3)
-IO.print("4") // expect: 4
+System.print("4") // expect: 4
diff --git a/test/timer/sleep_return.wren b/test/timer/sleep_return.wren
index 6b6484d2..ada6cca5 100644
--- a/test/timer/sleep_return.wren
+++ b/test/timer/sleep_return.wren
@@ -1,3 +1,3 @@
 import "timer" for Timer
 
-IO.print(Timer.sleep(0)) // expect: null
+System.print(Timer.sleep(0)) // expect: null
diff --git a/test/timer/sleep_zero.wren b/test/timer/sleep_zero.wren
index 2240ea2c..d56cfb08 100644
--- a/test/timer/sleep_zero.wren
+++ b/test/timer/sleep_zero.wren
@@ -2,22 +2,22 @@ import "scheduler" for Scheduler
 import "timer" for Timer
 
 Scheduler.add {
-  IO.print("a before")
+  System.print("a before")
   Timer.sleep(0)
-  IO.print("a after")
+  System.print("a after")
 }
 
 Scheduler.add {
-  IO.print("b before")
+  System.print("b before")
   Timer.sleep(0)
-  IO.print("b after")
+  System.print("b after")
 }
 
-IO.print("main")
+System.print("main")
 Timer.sleep(0) // This is enough to let the other fibers run to their sleep.
-IO.print("main after")
+System.print("main after")
 Timer.sleep(0) // And now their sleeps complete.
-IO.print("done")
+System.print("done")
 
 // expect: main
 // expect: a before