anchor.diff:  
   /// A function definition, consisting of parameters and a body.  The parameters
   /// include a distinguished continuation parameter.
  -class FunctionDefinition extends Node {
  +class FunctionDefinition extends Node implements InteriorNode {
     final FunctionElement element;
     final Continuation returnContinuation;
     final List<Parameter> parameters;
  -  final Expression body;
  +  Expression body;
     final List<ConstDeclaration> localConstants;
   
     /// Values for optional parameters.
  
positive.code: ///
  /// Closure variables without a declaring [SetClosureVariable] are implicitly
  /// declared at the entry to the [variable]'s enclosing function.
  class SetClosureVariable extends Expression {
    final Local variable;
    final Reference value;
    Expression body;
  
negative.code: abstract class Invoke {
    Selector get selector;
    List<Reference> get arguments;
  }
  
  /// Represents a node with a child node, which can be accessed through the
  /// `body` member. A typical usage is when removing a node from the CPS graph:
  ///
  ///     Node child          = node.body;
  ///     InteriorNode parent = node.parent;
  ///
  ///     child.parent = parent;
  ///     parent.body  = child;
  abstract class InteriorNode implements Node {
    Expression body;
  }
  
  /// Invoke a static function or static field getter/setter.
  