SafeFizzBuzz

gistfile1.scala

object SafeFizzBuzz extends scalaz.effect.SafeApp {
  import scalaz._
  import scalaz.effect._
  import scalaz.std.string._

  override def run(args: ImmutableArray[String]): IO[Unit] = {
    def int2answer(i: Int) =
      if (i % 3 == 0 && i % 5 == 0) Some("fizzbuzz")
      else if (i % 3 == 0) Some("fizz")
      else if (i % 5 == 0) Some("buzz")
      else None

    lazy val mainLoop: IO[Unit] = for {
      _ <- IO.putStr("Enter a number (done to finish): ")
      line <- IO.readLn.map(_.stripLineEnd)
      _ <-
        if (line == "done") IO.ioUnit
        else for {
          _ <- parseInt(line).fold(
            _ => IO.putStrLn(s"$line was not a number!"),
            int2answer(_).fold(IO.ioUnit)(IO.putStrLn)
          )
          _ <- mainLoop
        } yield ()
    } yield ()

    mainLoop
  }
}