Make string interpolations be compile-time-constants.

frog/leg/compile_time_constants.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class Constant implements Hashable {
   const Constant();
 
   bool isNull() => false;
   bool isBool() => false;
   bool isTrue() => false;
@@ skipping 752 matching lines @@
 
   Constant visitLiteralNull(LiteralNull node) {
     return new NullConstant();
   }
 
   Constant visitLiteralString(LiteralString node) {
     return new StringConstant(node.dartString);
   }
 
   Constant visitStringJuxtaposition(StringJuxtaposition node) {
-    if (!node.isInterpolation) {
-      return new StringConstant(node.dartString);
-    }
-    return super.visitStringJuxtaposition(node);
+    StringConstant left = evaluate(node.first);
+    StringConstant right = evaluate(node.second);
+    return new StringConstant(new DartString.concat(left.value, right.value));
+  }
+
+  Constant visitStringInterpolation(StringInterpolation node) {
+    StringConstant initialString = evaluate(node.string);
+    DartString accumulator = initialString.value;
+    for (StringInterpolationPart part in node.parts) {
+      Constant expression = evaluate(part.expression);
+      DartString expressionString;
+      if (expression.isNum() || expression.isBool()) {
+        Object value = expression.value;
+        expressionString = new DartString.literal(value.toString());
+      } else if (expression.isString()) {
+        expressionString = expression.value;
+      } else {
+        error(part.expression);
+      }
+      accumulator = new DartString.concat(accumulator, expressionString);
+      StringConstant partString = evaluate(part.string);
+      accumulator = new DartString.concat(accumulator, partString.value);
+    };
+    return new StringConstant(accumulator);
   }
 
   // TODO(floitsch): provide better error-messages.
   Constant visitSend(Send send) {
     Element element = elements[send];
     if (Elements.isStaticOrTopLevelField(element)) {
       if (element.modifiers === null ||
           !element.modifiers.isFinal()) {
         error(send);
       }
@@ skipping 236 matching lines @@
     return constant;
   }
 
   error(Node node) {
     // TODO(floitsch): get the list of constants that are currently compiled
     // and present some kind of stack-trace.
     MessageKind kind = MessageKind.NOT_A_COMPILE_TIME_CONSTANT;
     compiler.reportError(node, new CompileTimeConstantError(kind, const []));
   }
 }