case object Ping
case object Pong
case object Stop

import scala.actors.Actor
import scala.actors.Actor._


class Ping(x: Int, pong: Actor) extends Actor {
  def act() {
    var pingsToGo = x
    pong ! Ping
    println("Ping numer: " + pingsToGo)
    while(true) {
      receive {
        case Pong =>
          if(pingsToGo != 0) {
            pingsToGo-=1
            println("Ping numer: " + pingsToGo)
            pong ! Ping
          } else {
            pong ! Stop
            exit()
          }
      }
    }
  }
}

class Pong extends Actor {
  def act() {
    while(true) {
      receive {
        case Ping =>
          print("Pong")
          sender ! Pong
        case Stop =>
          println("Koniec.")
          exit()
      }
    }
  }
}

val pong = new Pong
val ping = new Ping(10, pong)
pong.start
ping.start