anchor.diff:  
   /// A function definition, consisting of parameters and a body.  The parameters
   /// include a distinguished continuation parameter.
  -class FunctionDefinition extends Node implements InteriorNode {
  +class FunctionDefinition extends Node {
     final FunctionElement element;
     final Continuation returnContinuation;
     final List<Parameter> parameters;
  -  Expression body;
  +  final Expression body;
     final List<ConstDeclaration> localConstants;
   
     /// Values for optional parameters.
  
positive.code: /// Continuations are normally bound by 'let cont'.  A continuation with no
  /// parameter (or body) is used to represent a function's return continuation.
  /// The return continuation is bound by the Function, not by 'let cont'.
  class Continuation extends Definition implements InteriorNode {
    final List<Parameter> parameters;
    Expression body = null;
  
  
negative.code: ///
  ///   let rec [variable] = [definition] in [body]
  ///
  class DeclareFunction extends Expression {
    final Local variable;
    final FunctionDefinition definition;
    Expression body;
  