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package examples.actors
import scala.actors.Actor
import scala.actors.Actor._
abstract class Producer[T] {
/** A signal that the next value should be produced. */
private val Next = new Object
/** A label for an undefined state of the iterators. */
private val Undefined = new Object
/** A signal to stop the coordinator. */
private val Stop = new Object
protected def produce(x: T) {
coordinator ! Some(x)
receive { case Next => }
}
protected def produceValues: Unit
def iterator = new Iterator[T] {
private var current: Any = Undefined
private def lookAhead = {
if (current == Undefined) current = coordinator !? Next
current
}
def hasNext: Boolean = lookAhead match {
case Some(x) => true
case None => { coordinator ! Stop; false }
}
def next: T = lookAhead match {
case Some(x) => current = Undefined; x.asInstanceOf[T]
}
}
private val coordinator: Actor = actor {
loop {
react {
case Next =>
producer ! Next
reply {
receive { case x: Option[_] => x }
}
case Stop =>
exit('stop)
}
}
}
private val producer: Actor = actor {
receive {
case Next =>
produceValues
coordinator ! None
}
}
}
object producers extends Application {
class Tree(val left: Tree, val elem: Int, val right: Tree)
def node(left: Tree, elem: int, right: Tree): Tree = new Tree(left, elem, right)
def node(elem: int): Tree = node(null, elem, null)
def tree = node(node(node(3), 4, node(6)), 8, node(node(9), 10, node(11)))
class PreOrder(n: Tree) extends Producer[Int] {
def produceValues = traverse(n)
def traverse(n: Tree) {
if (n != null) {
produce(n.elem)
traverse(n.left)
traverse(n.right)
}
}
}
class PostOrder(n: Tree) extends Producer[Int] {
def produceValues = traverse(n)
def traverse(n: Tree) {
if (n != null) {
traverse(n.left)
traverse(n.right)
produce(n.elem)
}
}
}
class InOrder(n: Tree) extends Producer[Int] {
def produceValues = traverse(n)
def traverse(n: Tree) {
if (n != null) {
traverse(n.left)
produce(n.elem)
traverse(n.right)
}
}
}
actor {
print("PreOrder:")
for (x <- new PreOrder(tree).iterator) print(" "+x)
print("\nPostOrder:")
for (x <- new PostOrder(tree).iterator) print(" "+x)
print("\nInOrder:")
for (x <- new InOrder(tree).iterator) print(" "+x)
print("\n")
}
}
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