Add support for sync* and yield

runtime/lib/core_patch.dart

Index: runtime/lib/core_patch.dart
===================================================================
--- runtime/lib/core_patch.dart	(revision 43415)
+++ runtime/lib/core_patch.dart	(working copy)
@@ -21,3 +21,49 @@
   static const List<String> _enum_names = null;
   String toString() => _enum_names[index];
 }
+
+
+class _SyncIterable extends IterableBase {
+  final moveNextFn;
+
+  const _SyncIterable(this.moveNextFn);
+
+  get iterator {
+    return new _SyncIterator(moveNextFn._clone());
+  }
+}
+
+class _SyncIterator implements Iterator {
+  var isYieldEach;

[srdjan, 2015/02/04 19:29:12]

Please add comment who sets isYieldEach. Also maybe add some comments to both
_SyncIterable and _SyncIterator.

[hausner, 2015/02/04 22:09:23]

Done.

+  var yieldEachIterator = null;
+  var current = null;

[srdjan, 2015/02/04 19:29:12]

I think null is the default initialization for all fields, you do not need to
explicitly do it.

[hausner, 2015/02/04 22:09:23]

Done.

+  var moveNextFn;

[srdjan, 2015/02/04 19:29:12]

Does the spec say anything about the type of moveNextFn? If so, please use type.

[hausner, 2015/02/04 22:09:23]

I don't want to use types. The type checks are unnecessary runtime overhead.

+
+  _SyncIterator(this.moveNextFn);
+
+  moveNext() {

[srdjan, 2015/02/04 19:29:12]

bool moveNext() {

[hausner, 2015/02/04 22:09:24]

Done.

+    if (moveNextFn == null) {
+      return false;
+    }
+    for(;;) {

[srdjan, 2015/02/04 19:29:12]

What is the advantage of "for(;;)" vs "while(true)"? (I find the later more
readable).

[hausner, 2015/02/04 22:09:23]

Done.

+      if (yieldEachIterator != null) {
+        if (yieldEachIterator.moveNext()) {
+          current = yieldEachIterator.current;
+          return true;
+        }
+        yieldEachIterator = null;
+      }
+      isYieldEach = false;
+      if (!moveNextFn(this)) {
+        moveNextFn = null;
+        current = null;
+        return false;
+      }
+      if (isYieldEach && (current is Iterable)) {
+        yieldEachIterator = current.iterator;
+        continue;
+      }
+      return true;    
+    }
+  }
+}