package coroutine

import scala.util.continuations._

abstract class Coroutine
{
    private var started = false         

    private var _session: Unit => Unit = null
    
    def act (): Unit @suspendable

    final def end (): Unit @suspendable = { _session = null } 

    final def start ()
    {
        reset { 
            started = true
            act () 
            end ()
        } // reset
    } // start

    final def resume () { _session () } 

    final def yyield (coroutine: Coroutine): Unit @suspendable = 
    {
        shift { 
            remaining: (Unit => Unit) => { 
                _session = remaining
                if (coroutine.started == false) {
                    coroutine.start()
                } else {
                    coroutine.resume()
                } // if
            }
        } // shift
    } // yyield

} // Coroutine

object CoroutineTest extends App
{
    class Cor1 extends Coroutine
    {
        def act (): Unit @suspendable = 
        {
            println ("Cor1: phase 1 ")
            yyield (cor2)
            println ("Cor1: phase 2")
            yyield (cor2)
        } // act
    } // Cor1

    class Cor2 extends Coroutine
    {
        def act (): Unit @suspendable = 
        {
            println ("Cor2: phase 1")
            yyield (cor1)
            println ("Cor2: phase 2")
        } // act
    } // Cor2

    val cor1 = new Cor1 ()
    val cor2 = new Cor2 ()

    println ("start coroutines")
    cor1.start ()                    

} // CoroutineTest