Scala term string parser

Parsify.scala

/**
 * @author Jay Taylor [@jtaylor]
 *
 * @date 2011-08-29
 *
 * @description Eventually I'd like to see this (or something even better)
 * included in the scala.sh library.
 */

trait Parsify {
    val parsifyTermExtractor = """([+-]?"([^"]|\\")+"|-?\S+)""".r
    val parsifyTermCleaner = """^[+-]?"?(.*?)"?$""".r

    val emptyTuple2OfStrings = (List[String](), List[String]())

    /** 
     * Parses (+|-)?("a b c"|def) term strings into a Tuple of positive and
     * negative elements.
     *
     * @return Tuple(List[String], List[String])
     * Note: ._1 = terms to include, ._2 = terms to exclude.
     */
    def parseTerms(terms: String): (List[String], List[String]) =
        Option(terms) match {
            case Some(terms) =>
                terms.trim.length match {
                  case 0 => emptyTuple2OfStrings
                  case n =>
                      val tokens = parsifyTermExtractor.findAllIn(terms).matchData map {
                          _.group(0)
                      } toList

                      def extractMatches(pred: String => Boolean): List[String] =
                          tokens filter { pred(_) } map {
                              parsifyTermCleaner.findFirstMatchIn(_).get group 1
                          } filter { _.length > 0 } toList

                      val must = extractMatches({ _.charAt(0) != '-' })

                      val mustNot = extractMatches({ _.charAt(0) == '-' })

                      (must, mustNot)
                }   

            case None => emptyTuple2OfStrings
        }   
}