initial sync*, part of #221

lib/src/codegen/js_metalet.dart

Index: lib/src/codegen/js_metalet.dart
diff --git a/lib/src/codegen/js_metalet.dart b/lib/src/codegen/js_metalet.dart
index daf7215d070df4ec632689f84e0f062ad3755832..87672ea43d8761ec3251b03028ecf83518700c7b 100644
--- a/lib/src/codegen/js_metalet.dart
+++ b/lib/src/codegen/js_metalet.dart
@@ -18,7 +18,7 @@ import 'js_names.dart' show TemporaryId;
 ///     (let* (x1=expr1, x2=expr2, t=x1[x2]) { x1[x2] = t + 1; t })
 ///
 /// [MetaLet] will simplify itself automatically when [toExpression],
-/// [toStatement], or [toReturn] is called.
+/// [toStatement], [toReturn], or [toYieldStatement] is called.
 ///
 /// * variables used once will be inlined.
 /// * if used in a statement context they can emit as blocks.
@@ -112,6 +112,14 @@ class MetaLet extends Expression {
     return _finishStatement(statements);
   }
 
+  Block toYieldStatement({bool star: false}) {
+    var statements = body
+        .map((e) =>
+            e == body.last ? e.toYieldStatement(star: star) : e.toStatement())
+        .toList();
+    return _finishStatement(statements);
+  }
+
   accept(NodeVisitor visitor) => toExpression().accept(visitor);
 
   void visitChildren(NodeVisitor visitor) {