def mkString[E](start: String, sep: String, end: String): Iteratee[E, String] = {

    def step(s: String, isFirst: Boolean)(input: Input[E]): Iteratee[E, String] = {
      input match {
        case Input.EOF => Done(s + end, Input.EOF)

        case Input.Empty => Cont(step(s, isFirst))

        case Input.El(e) => { val s1 = if(isFirst) { s + e.toString } else { s + sep + e.toString }; Cont[E, String](i => step(s1, false)(i)) }
      }
    }

    Cont(step(start, true))

  }