anchor.diff:  
     // TODO rename sendString
     // TODO send with List<int>
  -  // TODO Future
     Future<bool> send(String data){
       // TODO check OPEN
       var completer = new Completer<bool>();
  
positive.code:       if (result != null) {
          // TODO return value ?
          _ttyFd = -1;
          _state = CLOSED;
          completer.complete(true);
        } else {
          completer.completeError("Unexpected error");
  
negative.code: 
    Future<bool> close(){
      // TODO check OPEN
      var completer = new Completer<bool>();
      var replyPort = new RawReceivePort();
      _servicePort.send([replyPort.sendPort, "close", _ttyFd]);
  