cli.scala

object cli extends App {

  val cli: IO[IOException, Unit] = for {
    _ <- putStrLn("0. To exit\n1. One\n2. Two\n3. Three\n4. Four\n")
    l <- getStrLn
    _ <- Try(l.toInt) match {
      case Success(c) => {
        if(c == 0) IO.now(())
        else if (c > 4) putStrLn(s"invalid input: " + c) *> cli
        else putStrLn(s"got number: " + c) *> cli
      }
      case Failure(ex) => putStrLn(s"got exception: " + ex) *> cli
    }
  } yield ()

  def run(args: List[String]): IO[Nothing, ExitStatus] =
    cli.attempt.map(_.fold(_ => 1, _ => 0)).map(ExitStatus.ExitNow(_))
}