Scala CPS learning

Demo1.scala

package demo

import scala.util.continuations._

object Demo1 {

  def main(args: Array[String]) {
    
    var cont: (Int=>String) = null
    
    println("before reset")
    
    reset {
      println("before shift")
      
      val result = shift { k: (Int=>String) =>
        cont = k
        println("inside shift")
      }
      
      println(s"after shift result = $result")
      result.toString
    }
    
    println("after reset")
    
    println(cont(5))

  }

}

Demo1U.scala

package demo

import scala.util.continuations._

object Demo1U {

  def main(args: Array[String]) {

    var cont: (Int => String) = null

    def resetBody(): ControlContext[Int, String, Unit] = {
      println("before shift")
      shiftR(fShift _).map(fResume _)
    }

    def fShift(k: Int => String) {
      cont = k
      println("inside shift")
    }

    def fResume(result: Int): Int = {
      println(s"after shift result = $result");
      result
    }

    println("before reset")
        
    val pkg = scala.util.continuations.`package`
    
    val method = pkg.getClass().getMethod("reset", classOf[Function0[_]])
    method.invoke(pkg, resetBody _)
    
    println("after reset")
    
    println(cont(5))

  }

}

Demo2.scala

package demo

import scala.util.continuations._

object Demo2{

  def main(args: Array[String]) {
    
    println("before reset")
    var cont: (Int=>String) = null
    
    var str: String = ""
    
    reset {
      
      var i = 0
      while(i < 2) {
        
        val hole: Int  = shift { k:(Int=>String) =>
          cont = k
          println(s"inside shift loop = $i")
          s"continue at loop = $i"
        }
        
        cont = null
        
        str = str + hole
        println(s"reset: loop=$i hole = $hole str = $str")
        i += 1
      }
      str
    }
    
    var i = 0
    while(cont != null) {
      i += 1
      println(s"cont($i) = ${cont(i)}");
      println(s"main: str=$str")
    }
    
    println(s"str = $str")

  }

}

Demo2U.scala

package demo

import scala.util.continuations._

object Demo2U {

  def main(args: Array[String]) {
    println("before reset")

    var cont: (Int => String) = null
    var str = ""

    object ResetBody extends Function0[ControlContext[String, String, String]] {

      var i = 0

      def apply() = {
        i = 0
        whileBody(i).map( _=>str)
      }
      
      def whileBody(i: Int): ControlContext[Unit, String, String] = {
        if (i < 2) {
          val cc = shiftR(fShift _).map(fResume _)
          cc.flatMap(_ => whileBody(i))
        } else
          shiftUnitR(())
      }

      def fShift(f: Int => String): String = {
        cont = f
        println(s"inside shift loop = $i")
        s"continue at loop = $i"
      }
      
      def fResume(hole: Int): Unit = {
        cont = null
        str = str + hole
        println(s"reset: loop=$i hole = $hole str = $str")
        i += 1
      }
    }

    val pkg = scala.util.continuations.`package`
    val method = pkg.getClass().getMethod("reset", classOf[Function0[_]])
    method.invoke(pkg, ResetBody)

    var i = 0
    while (cont != null) {
      i += 1
      println(s"cont($i) = ${cont(i)}");
      println(s"main: str=$str")
    }

    println(s"str = $str")

  }
}