def rep1[T](first: => Parser[T], p: => Parser[T]): Parser[List[T]]

  def rep1[T](first: => Parser[T], p: => Parser[T]): Parser[List[T]] = Parser{ in0 =>
    val xs = new scala.collection.mutable.ListBuffer[T]
    var in = in0

    var res = first(in)

    while(res.successful) {
      xs += res.get
      in = res.next
      res = p(in)
    }

    // assert(res.isInstanceOf[NoSuccess])

    if (!xs.isEmpty) {
      // the next parser should start parsing where p failed, 
      // since `!p(in).successful', the next input to be consumed is `in'
      Success(xs.toList, in)  // TODO: I don't think in == res.next holds
    }
    else {
      Failure(res.asInstanceOf[NoSuccess].msg, in0)
    }
  }

  def rep1[T](first: => Parser[T], p: => Parser[T]): Parser[List[T]] = Parser{ in0 =>
    val xs = new scala.collection.mutable.ListBuffer[T]
    var in = in0
    var res = first(in)
    while(res.successful) {
      xs += res.get
      in = res.next
      res = p(in)
    }
    
    res match {
      case e: Error => e
      case _  => if (!xs.isEmpty) Success(xs.toList, in) else Failure(res.asInstanceOf[NoSuccess].msg, in0) 
    }
  }