Make null falsey.

benchmark/fib.wren

@@ -1,8 +1,5 @@
 var fib = fn(n) {
-  if (n < 2) {
-    return n
-  }
-
+  if (n < 2) return n
   return fib.call(n - 1) + fib.call(n - 2)
 }
 

src/wren_vm.c

@@ -997,9 +997,7 @@ static bool runInterpreter(WrenVM* vm)
       int offset = READ_SHORT();
       Value condition = POP();
 
-      // False is the only falsey value.
-      // TODO: Null should be falsey too.
-      if (IS_FALSE(condition)) ip += offset;
+      if (IS_FALSE(condition) || IS_NULL(condition)) ip += offset;
       DISPATCH();
     }
 
@@ -1008,18 +1006,16 @@ static bool runInterpreter(WrenVM* vm)
       int offset = READ_SHORT();
       Value condition = PEEK();
 
-      // False is the only falsey value.
-      // TODO: Null should be falsey too.
-      if (!IS_FALSE(condition))
-      {
-        // Discard the condition and evaluate the right hand side.
-        POP();
-      }
-      else
+      if (IS_FALSE(condition) || IS_NULL(condition))
       {
         // Short-circuit the right hand side.
         ip += offset;
       }
+      else
+      {
+        // Discard the condition and evaluate the right hand side.
+        POP();
+      }
       DISPATCH();
     }
 
@@ -1028,9 +1024,7 @@ static bool runInterpreter(WrenVM* vm)
       int offset = READ_SHORT();
       Value condition = PEEK();
 
-      // False is the only falsey value.
-      // TODO: Null should be falsey too.
-      if (IS_FALSE(condition))
+      if (IS_FALSE(condition) || IS_NULL(condition))
       {
         // Discard the condition and evaluate the right hand side.
         POP();

test/for/truth.wren

@@ -0,0 +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
+
+// Everything else is true.
+if (true) IO.print(true) // expect: true
+if (0) IO.print(0) // expect: 0
+if ("") IO.print("empty") // expect: empty

test/if.wren

@@ -1,28 +0,0 @@
-// Evaluate the 'then' expression if the condition is true.
-if (true) IO.print("good") // expect: good
-if (false) IO.print("bad")
-
-// 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
-
-// Allow blocks for branches.
-if (true) { IO.print("block") } // expect: block
-if (false) null else { IO.print("block") } // expect: block
-
-// Assignment in if condition.
-var a = false
-if (a = true) IO.print(a) // expect: true
-
-// Newline after "if".
-if
-(true) IO.print("good") // expect: good
-
-// Newline after "else".
-if (false) IO.print("bad") else
-IO.print("good") // expect: good
-
-// Only false is falsy.
-if (0) IO.print(0) // expect: 0
-if (null) IO.print(null) // expect: null
-if ("") IO.print("empty") // expect: empty

test/if/dangling_else.wren

@@ -0,0 +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")

test/if/else.wren

@@ -0,0 +1,10 @@
+// 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
+
+// Allow block body.
+if (false) null else { IO.print("block") } // expect: block
+
+// Newline after "else".
+if (false) IO.print("bad") else
+IO.print("good") // expect: good

test/if/if.wren

@@ -0,0 +1,14 @@
+// Evaluate the 'then' expression if the condition is true.
+if (true) IO.print("good") // expect: good
+if (false) IO.print("bad")
+
+// Allow block body.
+if (true) { IO.print("block") } // expect: block
+
+// Assignment in if condition.
+var a = false
+if (a = true) IO.print(a) // expect: true
+
+// Newline after "if".
+if
+(true) IO.print("good") // expect: good

test/if/truth.wren

@@ -0,0 +1,32 @@
+class Iter {
+  new(value) { _value = value }
+  iterate(iterator) { return _value }
+  iteratorValue(iterator) { return "value" }
+}
+
+// False and null are false.
+for (n in new Iter(false)) {
+  IO.print("bad")
+  break
+}
+
+for (n in new Iter(null)) {
+  IO.print("bad")
+  break
+}
+
+// Everything else is true.
+for (n in new Iter(true)) {
+  IO.print("true") // expect: true
+  break
+}
+
+for (n in new Iter(0)) {
+  IO.print(0) // expect: 0
+  break
+}
+
+for (n in new Iter("")) {
+  IO.print("string") // expect: string
+  break
+}

test/logical_operator/and.wren

@@ -18,9 +18,3 @@ IO.print(true) && // expect: true
 // Swallow a trailing newline.
 IO.print(true &&
     true) // expect: true
-
-// Only false is falsy.
-IO.print(0 && true) // expect: true
-IO.print(null && true) // expect: true
-IO.print("" && true) // expect: true
-IO.print(false && true) // expect: false

test/logical_operator/and_truth.wren

@@ -0,0 +1,8 @@
+// False and null are false.
+IO.print(false && "bad") // expect: false
+IO.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

test/logical_operator/or.wren

@@ -18,9 +18,3 @@ IO.print(false) || // expect: false
 // Swallow a trailing newline.
 IO.print(true ||
     true) // expect: true
-
-// Only false is falsy.
-IO.print(0 || true) // expect: 0
-IO.print(null || true) // expect: null
-IO.print(("" || true) == "") // expect: true
-IO.print(false || true) // expect: true

test/logical_operator/or_truth.wren

@@ -0,0 +1,8 @@
+// False and null are false.
+IO.print(false || "ok") // expect: ok
+IO.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

test/while/truth.wren

@@ -0,0 +1,26 @@
+// False and null are false.
+while (false) {
+  IO.print("bad")
+  break
+}
+
+while (null) {
+  IO.print("bad")
+  break
+}
+
+// Everything else is true.
+while (true) {
+  IO.print("true") // expect: true
+  break
+}
+
+while (0) {
+  IO.print(0) // expect: 0
+  break
+}
+
+while ("") {
+  IO.print("string") // expect: string
+  break
+}