Escape all in String

Escape.scala

object Lucene {

  object Escape extends (String => String) {

    private val prefix: Char => PartialFunction[Char, String] = c => { case `c` => s"\\$c" }

    private val escapist: PartialFunction[Char, String] = prefix('\\') orElse
                                                          prefix('+') orElse
                                                          prefix('-') orElse
                                                          prefix('!') orElse
                                                          { case c => s"$c" }

    def apply(s: String): String = s map(escapist) mkString
  }
}

Just looking for a nice way to implement lucene.QueryParserUtil.escape