anchor.diff:  
       var bodyBlock = currentBlock = make.emptyBlock();
       visit(node.body)(rk, ek, () {
  -      addStatement(make.assignmentExpression(make.identifier(trampolineName),
  -          make.identifier(continueName)));
  +      _addTrampoline(trampolineName, make.identifier(continueName));
       });
   
       var loopBlock = currentBlock = make.emptyBlock();
  
positive.code:       var savedBlock = currentBlock;
        var bodyBlock = currentBlock = make.emptyBlock();
        visit(node.body)(rk, ek, () {
          addStatement(make.assignmentExpression(make.identifier(trampolineName),
              make.identifier(continueName)));
        });
  
        currentBlock = savedBlock;
  
negative.code:     addStatement(
          make.functionDeclarationStatement(continueName, [], continueBlock));
      visit(node.body)(rk, ek, () {
        _addTrampoline(trampolineName, make.identifier(continueName));
      });
  
      breakTargets = savedBreakTargets;
  