问解析器组合器处理与可选解析器的交替

EN

def compose[X, Y](p: Parser[Option[X]], q: Parser[Y]): Parser[Either[X, Y]] = Parser {
  in =>
    p(in) match {
      case s@this.Success(Some(_), _) => s map (xo => Left(xo.get))
      case _ => q(in) match {
        case s@this.Success(_, _) => s map (x => Right(x))
        case _ => this.Failure("combine: failed", in)
      }
    }
}

implicit class ParserOps[X](p: Parser[Option[X]]) {
  def ?|[Y](q: => Parser[Y]): Parser[Either[X, Y]] = compose(p, q)
}

// Example of usage
def anadicTerm: Parser[AnadicTerm] = (maybeNumber ?| anadicOperator) ^^ {
  case Left(x: Number) => debug("anadicTerm (Number)", AnadicTerm(Right(x)))
  case Right(x: String) => debug("anadicTerm (String)", AnadicTerm(Left(x)))
}