anchor.diff:  setData(key, value) async {
     print("\t" + key + " ← " + value);
     data[key] = value;
  +  if (changeFutures.containsKey(key)) {
  +    changeFutures[key].complete(value);
  +    changeFutures.remove(key);
  +  }
     await new File(persistanceFileName).writeAsString(JSON.encode(data));
   }
   
  
positive.code: import "dart:convert";
  import 'dart:io';
  
  
negative.code: \tport\tdefault: $port""";
  
  Map<String, String> data = new Map<String, String>();
  Map<String, Completer> changeFutures = new Map<String, Completer>();
  
  main(List<String> args) async {
    try {
  