Simple extractor example

scala> object PositiveInt {
     |   def unapply (input : String) = try { if (input.toInt > 0) Some(input.toInt) else None } catch { case _ ⇒ None }
     | }
defined module PositiveInt

scala> List("foo","bar","14") match {                                                         
     |   case group :: user :: PositiveInt(id) :: Nil ⇒ println("%s:%s (%d)".format(group, user, id))
     |   case _ ⇒ // NOP                                                                             
     | }
foo:bar (14)