Implement for-in.

frog/leg/lib/core.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 void print(var obj) {
   obj = obj.toString();
   var hasConsole = JS("bool", @"typeof console == 'object'");
   if (hasConsole) {
     JS("void", @"console.log($0)", obj);
   } else {
@@ skipping 277 matching lines @@
     return UNINTERCEPTED(value.toString());
   }
   if (JS("bool", @"$0 === 0 && (1 / $0) < 0", value)) {
     return "-0.0";
   }
   if (value === null) return "null";
   return JS("string", @"String($0)", value);
 }
 
 
+builtin$iterator$0(var receiver) {
+  if (isJSArray(receiver)) {
+    return new ListIterator(receiver);
+  }
+  return UNINTERCEPTED(receiver.iterator());
+}
+
+
 bool isInt(var v) {
   return JS("bool", @"($0 | 0) === $1", v, v);
 }
 
+/* Include when interfaces are implemented
+interface Iterable<T> {
+  Iterator<T> iterator();
+}
+
+interface Iterator<T> {
+  bool hasNext();
+  T next();
+}
+*/
 class int {}
 class double {}
 class String {}
 class bool {}
 class Object {}
-class List<T> {
+class List<T> /* implements Iterable<T> */ {
   static void _checkConstructorInput(n) {
     // TODO(ngeoffray): Inline once we support optional parameters or
     // bailout.
     if (!isInt(n)) throw "Invalid argument";
     if (n < 0) throw "Negative size";
   }
 
   factory List(n) {
     // TODO(ngeoffray): Adjust to optional parameters.
     if (JS("bool", @"$0 === (void 0)", n)) return JS("Object", @"new Array()");
     _checkConstructorInput(n);
     return JS("Object", @"new Array($0)", n);
   }
 }
 
+class ListIterator<T> /* implements Iterator<T> */ {

[ngeoffray, 2012/01/11 10:09:22]

I'd prefer calling it ForeignListIterator.

+  int i;
+  List<T> list;
+  ListIterator(List<T> list) : this.list = list, i = 0;
+  bool hasNext() => i < JS("int", @"$0.length", list);
+  T next() {
+    var value = JS("Object", @"$0[$1]", list, i);
+    i += 1;
+    return value;
+  }
+}
+
 class Expect {
   static void equals(var expected, var actual) {
     if (expected == actual) return;
     _fail('Expect.equals(expected: <$expected>, actual:<$actual> fails.');
   }
 
   static void fail(String message) {
     _fail("Expect.fail('$message')");
   }
 
@@ skipping 47 matching lines @@
     } else {
       return
         JS("num", @"Math.floor($0 + (Date.now() - $1))", elapsedMs, startMs);
     }
   }
 
   int frequency() {
     return 1000;
   }
 }