package examples.actorsimport scala.actors.Actor._import scala.actors.{Channel, OutputChannel}/** @author Philipp Haller @version 1.1, 09/21/2007 */object fringe extends Application {  abstract class Tree  case class Node(left: Tree, right: Tree) extends Tree  case class Leaf(v: Int) extends Tree  case class CompareFringe(t1: Tree, t2: Tree)  case class ComputeFringe(t1: Tree, atoms: OutputChannel[Option[Leaf]])  case class Equal(atom1: Option[Leaf], atom2: Option[Leaf])  case class Extract(tree: Tree)  val comparator = actor {    val extractor1 = actor(extractorBehavior())    val extractor2 = actor(extractorBehavior())    val ch1 = new Channel[Option[Leaf]]    val ch2 = new Channel[Option[Leaf]]    loop {      react {        case CompareFringe(tree1, tree2) =>          extractor1 ! ComputeFringe(tree1, ch1)          extractor2 ! ComputeFringe(tree2, ch2)          self ! Equal(ch1.?, ch2.?)        case Equal(atom1, atom2) =>          if (atom1 == atom2) atom1 match {            case None =>              println("same fringe")              exit()            case _ =>              self ! Equal(ch1.?, ch2.?)          } else {            println("fringes differ")            exit()          }      }    }  }  val extractorBehavior = () => {    var output: OutputChannel[Option[Leaf]] = null    loop {      react {        case ComputeFringe(tree, leafSink) =>          output = leafSink          self ! Extract(tree)        case Extract(tree) => tree match {          case atom @ Leaf(_) =>            output ! Some(atom)            sender ! 'Continue          case Node(left, right) =>            val outer = self            val outerCont = sender            val cont = actor {              react {                case 'Continue =>                  outer.send(Extract(right), outerCont)              }            }            self.send(Extract(left), cont)        }        case 'Continue =>          output ! None          exit()      }    }  }  comparator ! CompareFringe(Node(Leaf(5), Node(Leaf(7), Leaf(3))),                Node(Leaf(5), Node(Leaf(7), Leaf(3))))}