Simple Future implementation with Haxe language

Future.hx

class Future {
  static final PENDING = 1;
  static final FULL = 2;

  var state:Int = PENDING;
  var result:Any = null;
  var next:Array<Any->Void> = [];
  
  public function new(){}

  public function start(starter:(Any->Void)->Void) {
    if (state != FULL) {
			starter(completer);
    }
    return this;
  }
  
  function completer(result:Any):Void {
		state = FULL;
    this.result = result;
    for (n in next)
      n(this.result);
    next = [];
  }
  
  public function then(onComplete:Any->Void):Future {
    // first attempt to build simple version
    
    if (state == PENDING) {
			next.push(onComplete);
    } else if (state == FULL){
			onComplete(this.result);
    }
    return this;
  }
    
    
  public function thenf(onComplete:Any->Any):Future {
		var f = new Future();
    if (state == PENDING) {
      next.push(result -> {
        var realResult:Any = result;
        if (realResult is Future) {
					realResult = (cast result:Future).result;
      	}
        var nextResult = onComplete(realResult);
        if (nextResult is Future) {
          (cast nextResult:Future).thenf(result -> {
						f.completer(result);
            return result;
          });
        }
      	else
      		f.completer(nextResult);
      });
    } 
    else if (state == FULL) {
			var nextResult = onComplete(this.result);
      if (nextResult is Future)
        return nextResult;
      else {
				var f = new Future();
        f.completer(nextResult);
        return f;
      }
    }
    return f;
  }
}

Test.hx

class Test {
  static function main() {
    // test it online: https://try.haxe.org/#F69A6783
    final wait = (delay:Int, ?id:String) -> {
      var stamp = Std.string(Math.fround(Timer.stamp()/1000));
      if (id!=null) stamp = id;
			trace('[$stamp]: wait for $delay ms...');
      return new Future().start(onComplete -> {
        Timer.delay(() -> {
					trace('[$stamp]: await of $delay ms completed');
      		onComplete(true);
      	}, delay);
  		});
  	};

		wait(1000)
      .thenf(_ -> wait(1000))
      .thenf(_ -> 42)
      .thenf(cast data -> trace('data: $data'))
      .thenf(_ -> wait(1000))
      .thenf(cast _ -> trace('Futures chain is done!')); 
  }
}