Software Crafters Barcelona 2018 - Open Space Monadic Refactor Workshop

accumulate.scala

import cats.{Id, Monad}
import cats.implicits._


object AccumulateConventional extends App {

  trait Console {
    def write(text: String): Unit
    def read(): String
  }

  def accumulateUntilNegativeNumber(counter: Int = 0)(console: Console): Unit = {
    console.write("Input a number pls")
    val input = console.read()
    val inputAsNumber = input.toInt
    if (inputAsNumber < 0) console.write(counter.toString)
    else accumulateUntilNegativeNumber(counter + inputAsNumber)(console)
  }

  val stdConsole = new Console {
    override def write(text: String): Unit = println(text)
    override def read(): String = scala.io.StdIn.readLine()
  }

  val fixFirstParameter: Console => Unit = accumulateUntilNegativeNumber(0)
  fixFirstParameter(stdConsole)
}



object AccumulateMonadic extends App {

  trait Console[P[_]] {
    def write(text: String): P[Unit]
    def read(): P[String]
  }

  def accumulateUntilNegativeNumber[P[_]](
    counter: Int = 0
  )(implicit console: Console[P], M: Monad[P]): P[Unit] =
    for {
      _ <- console.write("Input a number pls")
      input <- console.read()
      inputAsNumber = input.toInt
      _ <- if (inputAsNumber < 0) console.write(counter.toString)
      else accumulateUntilNegativeNumber(counter + inputAsNumber)
    } yield ()

  object Console {
    implicit object IdConsole extends Console[Id] {
      override def write(text: String): Unit = println(text)
      override def read(): String = scala.io.StdIn.readLine()
    }
  }

  case class IOState(toBeRead: List[String], written: List[String])

  type ConsoleTransformer[T] = IOState => (IOState, T)

  object IOState{
    implicit object ConsoleTransformerIO extends Console[ConsoleTransformer]{
      def write(text: String): ConsoleTransformer[Unit] = ???
      def read(): ConsoleTransformer[String] = {
        case IOState(head :: tail, written) =>
          (IOState(tail : List[String], written : List[String]), head : String)
    }
  }

  accumulateUntilNegativeNumber(0)
}