Single digit parser

single_digit_parser.scala

trait BencodeParser extends Parsers with BencodeConstants {

  type Elem = Byte

  implicit def charToParser(ch: Char) = elem(ch.toByte)

  def delimitedBy[A](left: Parser[Byte], right: Parser[Byte])(p: Parser[A]): Parser[A] = left ~> p <~ right

  def single_digit = new Parser[String] {

    val re = """\d""".r

    def apply(in: Input) = {
      if (in.atEnd) Failure("End of input reached", in)
      else {
        //Specification says numbers are coded in ASCII
        val n = new String(Array(in.first.asInstanceOf[Byte]), DEFAULT_NUMBER_ENCODING)
        re.findFirstIn(n) map (Success(_, in.rest)) getOrElse (Failure(s"'$n' is not a number", in))
      }
    }
  } named ("digit")
}