anchor.diff:  // See the License for the specific language governing permissions and
   // limitations under the License.
   
  -interface Action {
  -  GameNode get target;
  -           set target(GameNode);
  -
  -  bool get done;
  -
  -  void start();
  -  void step(num dt);
  -  void stop();
  -
  -  Action operator +(Action action);
  -  Action operator |(Action action);
  -}
  -
  -abstract class AbstractAction implements Action {
  +abstract class Action {
     GameNode target;
     bool done = false;
   
  
positive.code:   }
  }
  
  abstract class InstantAction extends AbstractAction {
    bool get done => true;
  
    void step(num dt) {}
  
negative.code:   }
  }
  
  class ActionSequence extends Action {
    List<Action> _actions;
    int _currentAction;
  
  