anchor.diff:     * The return value is a future which will fire with a list of results from
      * all signal handlers.
      */
  -  Future<List> emit(dynamic argument) {
  +  Future<List> emit(T argument) {
       var results = <Future>[];
       for (Callback subscription in subscriptions) {
         var result = subscription(argument);
  
positive.code:   /**
     * Connects a callback to this signal.
     */
    on(Callback callback) => subscriptions.add(callback);
  
  }
negative.code:  *     > Results of callbacks: [1, 1]
   *
   */
  class Signal<T> {
  
    final List<Callback> subscriptions = <Callback>[];
  
  