Simple functional getopt in Scala

Question

def main(args: Array[String]) {
  if (args.length == 0) println(usage)
  val argList = args.toList
  type OptionMap = Map[Symbol, Any]

  def nextOption(map: OptionMap, list: List[String]): OptionMap = {
    list match {
      case Nil => map
      case "-h" | "--help" :: tail => usage(); sys.exit(0)
      case "-p" | "--port" :: option :: tail => nextOption(map ++ Map('port -> option.toInt), tail)
  }
}

Is there any way to catch more head values in List? This code generates

type mismatch;
   found   : String("-h")
   required: List[String]
        case "-h" | "--help" :: tail => usage(); sys.exit(0)
             ^

possible duplicate: Best way to parse command-line parameters?

score 9 · Accepted Answer · answered Apr 17 '15 at 18:07

9

Just wrap the code in parentheses:

case ("-h" | "--help") :: tail => usage(); sys.exit(0)

Without the parentheses, the compiler interprets the code as

case ("-h") | ("--help" :: tail) => usage(); sys.exit(0)

which is not want you want.

answered Apr 17 '15 at 18:07

kiritsuku

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That's pretty neat, I actually didn't realize that syntax was valid. – Zeimyth Apr 17 '15 at 18:31

score 3 · Answer 2 · answered Apr 17 '15 at 17:58

Scala's pattern matching allows you to store a match in a variable and then perform conditional checks on that variable.

list match {
  case Nil => map
  case x :: tail if x == "-h" || x == "--help" => usage(); sys.exit(0)
  case y :: option :: tail if y == "-p" || y == "--port" => nextOption(map ++ Map('port -> option.toInt), tail)
}

Simple functional getopt in Scala

2 Answers2