monadTupoIO.scala

case class TupoIO[A](a: A, out: String) {
  def map[B](fun: A => B): TupoIO[B] = TupoIO(fun(a), out)
  def flatMap[B](fun: A => TupoIO[B]): TupoIO[B] = {
    val res = fun(a)
    TupoIO(res.a, out + res.out)
  }
  override def toString = out + a.toString
}

object TupoIO {
  def point[A](a: A): TupoIO[A] = TupoIO(a, "")
}

object monadTupoIO {

  def a(x: String): Double = { println("in A"); x.toDouble }
  def b(y: Double): Int = { println("in B"); y.toInt + 2 }

  def fa(x: String): TupoIO[Double] = TupoIO(x.toDouble, "in A\n")
  def fb(y: Double): TupoIO[Int] = TupoIO(y.toInt + 2, "in B\n")

  def main(args: Array[String]) {
    println((a _ andThen b _)("1.1"))

    import TupoIO._
    println(point("1.1").flatMap(fa).flatMap(fb))
  }
}