Avoid nested pattern match with Either

result.txt

> scala UseEither some
some success
> scala UseEither none
failure
> scala UseEither hoge
java.lang.Exception: example exception

UseEither.scala

object UseEither {
  def doSomething(arg: String): Either[Throwable, Option[String]] = arg match {
    case "none" => Right(None)
    case "some" => Right(Some("some"))
    case _ => Left(new Exception("example exception"))
  }

  def main(args: Array[String]) {
    val somethingEither = for {
      s <- doSomething(args(0)).right
    } yield s.map(_ + " success").getOrElse("failure")

    println(somethingEither.fold(
      l => l.toString,
      r => r
    ))
  }
}