From 7cc5c06947e40236ee16a6a09d3de524183fda86 Mon Sep 17 00:00:00 2001
From: Philipp Haller <hallerp@gmail.com>
Date: Fri, 2 Feb 2007 15:17:51 +0000
Subject: Cleaned-up actor examples.

---
 docs/examples/actors/producers.scala | 113 +++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 docs/examples/actors/producers.scala

(limited to 'docs/examples/actors/producers.scala')

diff --git a/docs/examples/actors/producers.scala b/docs/examples/actors/producers.scala
new file mode 100644
index 0000000000..7e8e34bf48
--- /dev/null
+++ b/docs/examples/actors/producers.scala
@@ -0,0 +1,113 @@
+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): 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]
+    }
+  }
+
+  private val coordinator: Actor = actor {
+    var continue = true
+    while (continue) {
+      receive {
+        case Next =>
+          producer ! Next
+          reply {
+            receive { case x: Option[_] => x }
+          }
+        case Stop => continue = false
+      }
+    }
+  }
+
+  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 {
+    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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