Adds typechecking of return values

frog/value.dart

Index: frog/value.dart
diff --git a/frog/value.dart b/frog/value.dart
index 88f93f42769417e3fa50646bfe3b878c9ba76927..476222928ff99c4ae5aedc1a318611c5f38d4048 100644
--- a/frog/value.dart
+++ b/frog/value.dart
@@ -37,6 +37,12 @@ class Value {
   /** Is this value a constant expression? */
   bool get isConst() => false;
 
+  /**
+   * A canonicalized form of the code. Two const expressions that result in the
+   * same instance should have the same [canonicalCode].
+   */
+  String get canonicalCode() => null;

[Siggi Cherem (dart-lang), 2011/11/11 08:23:53]

maybe this should throw an error in this case?

+
   // TODO(jimhug): Fix these names once get/set are truly pseudo-keywords.
   //   See issue #379.
   Value get_(MethodGenerator context, String name, Node node) {
@@ -328,7 +334,15 @@ class Value {
     // We rely on the fact that calling an undefined method produces a JS
     // TypeError. Alternatively we could define fallbacks on Object that throw.
     String check;
-    if (toType.library.isCore && toType.typeofName != null) {
+    if (toType.isVoid) {
+      check = '\$assert_void($code)';
+      if (toType.typeCheckCode == null) {

[jimhug, 2011/11/11 15:02:02]

Hmm, I'd rather not see this code sitting in value.dart.  I'll try to clean this
up with my next round of value changes - please let me do the cleanup here to
minimize conflicts <smile>.

+        toType.typeCheckCode = '''
+function \$assert_void(x) {
+  return x == null ? x : x.is\$void(); // throws TypeError
+}''';
+      }
+    } else if (toType.library.isCore && toType.typeofName != null) {
       check = '\$assert_${toType.name}($code)';
 
       if (toType.typeCheckCode == null) {