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import scala.actors._
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
protected def produce(x: T): unit = {
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]
}
}
case object Stop
class StopException extends Throwable
/** A thread-based coordinator */
private val coordinator: Actor = actor {
try {
while (true) {
receive {
case Next =>
producer ! Next
reply {
receive { case x: Option[_] => x }
}
case Stop => throw new StopException
}
}
} catch { case _: StopException => }
}
private val producer: Actor = actor {
receive {
case Next =>
produceValues
coordinator ! None
}
}
}
object Test extends Application {
def from(m: int, n: int) = new Producer[int] {
def produceValues = for (val i <- m until n) produce(i)
}
// note that it works from the main thread
val it = from(1, 10).iterator
while (it.hasNext) {
Console.println(it.next)
}
}
object Test2 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)
}
}
}
Debug.level = 3
// note that it works from the main thread
Console.print("PreOrder:")
for (val x <- new PreOrder(tree).iterator) Console.print(" "+x)
Console.print("\nPostOrder:")
for (val x <- new PostOrder(tree).iterator) Console.print(" "+x)
Console.print("\nInOrder:")
for (val x <- new InOrder(tree).iterator) Console.print(" "+x)
Console.print("\n")
}
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