cleanup to Value - fix for StringEscapesTest

frog/scripts/tree_gen.py

 #!/usr/bin/env python
 # Copyright (c) 2011, 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.
 
 '''Generates the many subtypes of Node as well as a NodeVisitor into
    tree.g.dart.'''
 
 from codegen import CodeWriter
 
@@ skipping 155 matching lines @@
 
   Expression('Is', 'bool isTrue, Expression x, TypeReference type'),
   Expression('Paren', 'Expression body'),
   Expression('Await', 'Expression body'),
 
   Expression('Dot', 'Expression self, Identifier name'),
   Expression('Var', 'Identifier name'),
 
   Expression('This'),
   Expression('Super'),
-  Expression('Null'),
 
-  Expression('Literal', 'var value, TypeReference type, String text'),
+  Expression('Literal', 'Value value'),
+
+  Expression('StringInterp', 'List<Expression> pieces'),
 
   # TODO(jimhug): Split into Simple and Qualified names
   TypeReference('Name',
     'bool isFinal, Identifier name, List<Identifier> names'),
 
   TypeReference('Generic',
     'TypeReference baseType, List<TypeReference> typeArguments, int depth'),
   TypeReference('Function',
     'bool isFinal, FunctionDefinition func'),
   TypeReference('Default', 'bool oldFactory, NameTypeReference baseType, '+
@@ skipping 44 matching lines @@
   cw.writeln('var output;')
   cw.writeln('TreePrinter(this.output) { output.printer = this; }')
   for node in nodes:
     node.writePrettyPrintMethod(cw)
     cw.writeln()
   cw.exitBlock('}')
 
   cw.writeToFile('tree')
 
 if __name__ == '__main__': main()