tricky_gen2Trav.scala

object Main {
  def toStreamWithThread[T](generator: (T=>Unit)=>Unit): Stream[T] = {
    val queue = new java.util.concurrent.SynchronousQueue[Option[T]]

    new Thread(
	    new Runnable {
	      def run() {
	        generator { (Some(_:T)) andThen (queue.put(_)) }
	        queue.put(None)
	      }
	    }   
    ).start()
    
    Stream.continually(queue.take).takeWhile(_.isDefined).map(_.get)
  }

  def toTraversable( data : (Int => Unit) => Unit) = {
    new Traversable[Int] {                     
      def foreach[U](f : Int => U) = {                 
         data( f(_) : Unit)                            
      }
    }
  }

  def main(args: Array[String]) {
    def data(block: Int => Unit) {
      for (i <- 0 to 10) {
        println("It is " + i + " here!")
        block(i)
      }
    }

    println("--- We want all ints")
    toTraversable(data).foreach { i =>
      println("and I like " + i + " very much!")
    }

    println("\n--- Now we want just first 7 ints (toStreamWithThread)")
    toStreamWithThread(data).take(7).foreach { i =>
      println("and I like " + i + " very much!")
    }

    println("\n--- Now we want just first 7 ints (toTraversable)")
    toTraversable(data).take(7).foreach { i =>
      println("and I like " + i + " very much!")
    }
  }
}


RESULT:


--- We want all ints
It is 0 here!
and I like 0 very much!
It is 1 here!
and I like 1 very much!
It is 2 here!
and I like 2 very much!
It is 3 here!
and I like 3 very much!
It is 4 here!
and I like 4 very much!
It is 5 here!
and I like 5 very much!
It is 6 here!
and I like 6 very much!
It is 7 here!
and I like 7 very much!
It is 8 here!
and I like 8 very much!
It is 9 here!
and I like 9 very much!
It is 10 here!
and I like 10 very much!

--- Now we want just first 7 ints (toStreamWithThread)
It is 0 here!
It is 1 here!
and I like 0 very much!
It is 2 here!
and I like 1 very much!
It is 3 here!
and I like 2 very much!
It is 4 here!
and I like 3 very much!
It is 5 here!
and I like 4 very much!
It is 6 here!
and I like 5 very much!
It is 7 here!
and I like 6 very much!

--- Now we want just first 7 ints (toTraversable)
It is 0 here!
It is 1 here!
It is 2 here!
It is 3 here!
It is 4 here!
It is 5 here!
It is 6 here!
It is 7 here!
and I like 0 very much!
and I like 1 very much!
and I like 2 very much!
and I like 3 very much!
and I like 4 very much!
and I like 5 very much!
and I like 6 very much!