Das Programmier-Spiel: nette Übungsaufgaben für zwischendurch

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import scala.actors.Actor
import scala.collection.immutable.HashMap

object Main {

  /**
   * @param args the command line arguments
   */

  def main(args: Array[String]) = {
    TransactionSystem ! ('create, "foo", 4000.)
    TransactionSystem ! ('create, "bar", 0.)
    TransactionSystem ! ('transfer, "foo", "bar", 2000.)
    println(TransactionSystem !? Tuple2('balance, "foo"))
    println(TransactionSystem !? Tuple2('balance, "bar"))
    TransactionSystem ! 'exit
  }

  object TransactionSystem extends Actor {
    start
    case class Account(val amount: Double)
    def act {
      act(HashMap[String, Account]())
    }
    def act(accs: HashMap[String, Account]): Unit = {
      react {
        case ('transfer, from: String, to: String, amount: Double)
          if(accs.contains(from) && accs.contains(to) &&
             accs(from).amount >= amount) => {
            act(accs.filter((acc) => acc != from && acc != to) ++
                HashMap(from -> Account(accs(from).amount - amount),
                        to -> Account(accs(to).amount + amount)))
        }
        case ('create, name: String, amount: Double) if(!accs.contains(name)) => act(accs ++ HashMap(name -> Account(amount)))
        case ('balance, name: String) if(accs.contains(name)) => reply(Some(accs(name).amount)); act(accs)
        case 'exit => exit
        case _ => println("Operation could not be completed."); act(accs)
      }
    }
  }

}