Error out on compile-time constants if equality is tested on bad types.

frog/leg/operations.dart

Index: frog/leg/operations.dart
diff --git a/frog/leg/operations.dart b/frog/leg/operations.dart
index 0f5ea51f6da5595c823b0b0c52191e0a2d913875..f9a7cd528dbbccef49a04a1e60afd8075d5d9f28 100644
--- a/frog/leg/operations.dart
+++ b/frog/leg/operations.dart
@@ -241,8 +241,12 @@ class EqualsOperation implements BinaryOperation {
       NumConstant leftNum = left;
       NumConstant rightNum = right;
       return new BoolConstant(leftNum.value == rightNum.value);
+    } else if (!left.isConstructedObject()) {

[Lasse Reichstein Nielsen, 2012/03/27 08:12:12]

I'd prefer 
  else if (left.isConstructedObject()) {
    return null;
  } else {
    ...
instead of the negative test. 
Generally, negative tests in if/else-if chains reduces readability *a lot*.

You can also drop the "else", since each branch returns.

[floitsch, 2012/03/28 00:25:21]

hehe. that's what I had before. After long hesitation I move the 'return null'
to the end. Reverted.
done.

+      // Unless we know that the user-defined object does not implement the
+      // equality operator we cannot fold here.
+      return new BoolConstant(left == right);
     }
-    return new BoolConstant(left == right);
+    return null;
   }
 }