Either

ScalaにもEitherあったんだな、と。

object Main {
  def foo(x : Int) : Either[String, Int] = x match {
    case 0 => Left("invalid arguments!")
    case _ => Right(x)
  }

  def result(a : Either[String, Int]) : Unit = a match {
    case Left(msg) => println("Error : " + msg)
    case Right(x) => println(x)
  }

  def main(args: Array[String]) {
    result(foo(0))
    result(foo(1))
  }
}

Error : invalid arguments!
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