DnsResolver.scala

import scala.actors._
import scala.actors.Actor._
import java.net.InetAddress

sealed abstract class DnsMessage
case class DnsRequest(name: String, sender: Actor) extends DnsMessage
case class DnsResponse(name: String, address: Option[InetAddress]) extends DnsMessage

class DnsResolver extends Actor {
  def act() {
    react {
      case DnsRequest(name, sender) =>
        sender ! handleDnsRequest(name)
    }
  }

  def handleDnsRequest(name: String): DnsResponse = {
    try {
      DnsResponse(name, Some(InetAddress.getByName(name)))
    } catch {
      case _: Exception =>
	DnsResponse(name, None)
    }
  }
}

object DnsPrinter extends Actor {
  def act() {
    loop {
      react {
	case DnsResponse(name, address) =>
	  println(name + ": "+ address)
	case Exit => exit()
      }
    }
  }
}

object Main {
  def main(args: Array[String]) {
     val names: List[String] = List(
      "www.hatena.ne.jp",
      "d.hatena.ne.jp",
      "www.google.co.jp",
      "foo.bar.baz"
    )
    
    DnsPrinter.start()
    for (name <- names) {
      val resolver = (new DnsResolver).start()
      resolver ! DnsRequest(name, DnsPrinter)
    }
    Thread.sleep(1000)
    DnsPrinter ! Exit
  }
}