rle_algorithm_in_scala.scala

import scala.util.Random

sealed trait Streamss[A, B]

object Streamss extends App {

  case class NeedInput[A, B](f: A => Streamss[A, B]) extends Streamss[A, B]

  case class HasOutput[A, B](b: B, s: Streamss[A, B]) extends Streamss[A, B]

  case class Done[A, B]() extends Streamss[A, B]


  // run length encoding using streams (http://haskell-for-readers.nomeata.de/#algebraic-data-types)
  def streams[A]: Streamss[A, (Int, A)] = NeedInput(rlestart[A])

  def rlestart[A]: A => Streamss[A, (Int, A)] = a => NeedInput(relCount(a, 1))

  def relCount[A](a: A, i: Int): A => Streamss[A, (Int, A)] =
    newA =>
      if (newA == a) NeedInput(relCount(a, i + 1)) else HasOutput((i, a), rlestart(newA))

  def run(s: Streamss[Int, (Int, Int)]): Unit =
    s match {
      case NeedInput(f) => run(f({
        Random.nextInt(2)
      }))
      case HasOutput(b, ss) => {
        println(b); run(ss)
      }
    }

  run(streams[Int])
}