Work in progress: changes to interpretation

frog/value.dart

Index: frog/value.dart
diff --git a/frog/value.dart b/frog/value.dart
index a1c7499c7cfb75b8e4bc86138662e5c8aa8e7236..7f20ce7f6c0bc3c2360e243ee5593a1463ebcb0d 100644
--- a/frog/value.dart
+++ b/frog/value.dart
@@ -66,11 +66,14 @@ class Value {
 
     // TODO(jmesserly): should use something like UnionValue and track the
     // precise set of types. For now we find the Type.union.
+    var t = Type.union(x.type, y.type);
+    if (t == x.type) return x;
+    if (t == y.type) return y;
 
     // TODO(jmesserly): What to do about code? Right now, we're intentionally
     // throwing it away because they aren't used in the current flow-insensitive
     // inference.
-    return new Value(Type.union(x.type, y.type), null, null);
+    return new Value(t, null, null);
   }
 
   Value _tryUnion(Value right) => null;
@@ -1474,3 +1477,4 @@ class VariableValue extends Value {
     return super.binop(kind, other, context, node);
   }
 }
+