It turns out "is" is just a normal overridable operator. Who knew?

test/language/is/is.wren

@@ -1,33 +0,0 @@
-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
-
-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.
-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.
-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".
-System.print(123 is
-  Num) // expect: true

test/language/is/nonclass_on_right.wren

@@ -1 +0,0 @@
-1 is false // expect runtime error: Right operand must be a class.

test/language/method/operators.wren

@@ -14,6 +14,7 @@ class Foo {
   !=(other) { "infix != " + other }
   &(other) { "infix & " + other }
   |(other) { "infix | " + other }
+  is(other) { "infix is " + other }
 
   ! { "prefix !" }
   ~ { "prefix ~" }
@@ -37,3 +38,4 @@ System.print(foo | "a") // expect: infix | a
 System.print(!foo) // expect: prefix !
 System.print(~foo) // expect: prefix ~
 System.print(-foo) // expect: prefix -
+System.print(foo is "a") // expect: infix is a