anchor.diff:      action.target = this.target;
       action.start();
     }
  -
  -  void stop() {
  -    action.stop();
  -  }
  +  
  +  void stop() => action.stop();
   
     void _interval(num t) {
       action._interval(pow(t, rate));
  
positive.code:   bool get done => false;
  
    Action();
  
    Action clone();
    void start();
    void step(num dt);
    void stop();
  
    reverse() {
      throw "Reverse not available";
    }
  
    Action operator +(Action action) {
      return new ActionSequence([this, action]);
    }
  
    Action operator |(Action action) {
      return new ActionSpawn([this, action]);
    }
  }
  
  abstract class InstantAction extends Action {
  
negative.code: 
    void stop() {}
  
    void _nextAction() {
      if (_currentAction == null) {
        _currentAction = 0;
      }
  