callback.scala

def callback(pubsub: PubSubMessage) = pubsub match {
  case S(channel, no) => println("subscribed to " + channel + " and count = " + no)
  case U(channel, no) => println("unsubscribed from " + channel + " and count = " + no)
  case M(channel, msg) => 
    msg match {
      // exit will unsubscribe from all channels and stop subscription service
      case "exit" => 
        println("unsubscribe all ..")
        r.unsubscribe

      // message "+x" will subscribe to channel x
      case x if x startsWith "+" => 
        val s: Seq[Char] = x
        s match {
          case Seq('+', rest @ _*) => r.subscribe(rest.toString){ m => }
        }

      // message "-x" will unsubscribe from channel x
      case x if x startsWith "-" => 
        val s: Seq[Char] = x
        s match {
          case Seq('-', rest @ _*) => r.unsubscribe(rest.toString)
        }

      // other message receive
      case x => 
        println("received message on channel " + channel + " as : " + x)
    }
}