gistfile1.scala

class Arbiter extends Actor {
  var occupants:List[String] = List()
  
  def addOccupant(who: String) = {
    occupants = occupants ::: List(who)
  }
  
  def removeOccupant(who: String) = {
    val (b, a) = occupants span (x => x != who)
    occupants = (b ::: a.drop(1))
  }

  def receive = {
    case EnterRoom(who) =>
    {
        addOccupant(who) // Add the person to the room list.
        sender ! Message(s"Hello there, $who!") // Send a greeting to the person.
    }
    case IntroduceRoom =>
    {
        var message = occupants.foldLeft("")((r,c) => r + (if (r == "") "" else if (occupants.last == c) " and " else ", ") + c)
        //var message = occupants.mkString(", ")
        sender ! Message(s"Everyone, meet: " + message)
    }
    case LeaveRoom(who) =>
    {
        sender ! Message(s"Bye, $who!") // Send a farewell to the person.
        removeOccupant(who) // Remove the person from the room list.
    }
  }
}