Add all the A tasks

Task/Active-object/Scala/active-object.scala

@@ -0,0 +1,48 @@
+object ActiveObject {
+
+  class Integrator {
+
+    import java.util._
+    import scala.actors.Actor._
+
+    case class Pulse(t: Double)
+    case class Input(k: Double => Double)
+    case object Output
+    case object Bye
+
+    val timer = new Timer(true)
+    var k: Double => Double = (_ => 0.0)
+    var s: Double = 0.0
+    var t0: Double = 0.0
+
+    val handler = actor {
+      loop {
+        react {
+          case Pulse(t1) => s += (k(t1) + k(t0)) * (t1 - t0) / 2.0; t0 = t1
+          case Input(k) => this.k = k
+          case Output => reply(s)
+          case Bye => timer.cancel; exit
+        }
+      }
+    }
+
+    timer.scheduleAtFixedRate(new TimerTask {
+      val start = System.currentTimeMillis
+      def run { handler ! Pulse((System.currentTimeMillis - start) / 1000.0) }
+    }, 0, 10) // send Pulse every 10 ms
+
+    def input(k: Double => Double) = handler ! Input(k)
+    def output = handler !? Output
+    def bye = handler ! Bye
+  }
+
+  def main(args: Array[String]) {
+    val integrator = new Integrator
+    integrator.input(t => Math.sin(2.0 * Math.Pi * 0.5 * t))
+    Thread.sleep(2000)
+    integrator.input(_ => 0.0)
+    Thread.sleep(500)
+    println(integrator.output)
+    integrator.bye
+  }
+}