UseScalaz.scala

object UseScalaz {


  def main(args: Array[String]): Unit = {

    import scalaz._


    case class Better(total: List[Int])

    def sum(i: Int): State[Better, Int] = State { b =>
      val result =  if(b.total.length > 1) 99 else  b.total.sum
      val newBetter =b.copy(total = i :: b.total)
      (newBetter, result)
    }

    val test = for {
      r1 <- sum(1)                 // first result
      state0 <- State.get[Better]  // state after first result                     
      r2 <- sum(2)                 // second result
      state1 <- State.get[Better]  // state after second result
      r3 <- sum(3)                 // third result
      state2 <-  State.get[Better] // state after third result
    } yield {
      (
        state0 :: state1 :: state2 :: Nil, // hey, I wanna see a list of the states as I did this, for debugging
        r1 :: r2 :: r3 :: Nil  // while I'm at it, lets look at a list of the results
      )

    }

    val someBetter = Better(Nil)
    
    // show the states
    test.run(someBetter)._2._1.zipWithIndex.foreach { case (v, i) => println(s"state$i - $v")}
    // show the results
    test.run(someBetter)._2._2.zipWithIndex.foreach { case (v, i) => println(s"result$i - $v")}
}}