either_monad.scala

class RichEither[L, R](val either: Either[L, R]) {
  def map[RR](f: R => RR): Either[L, RR] = either match {
    case Left(l) => Left(l)
    case Right(r) => Right(f(r))
  }
  def flatMap[RR](f: R => Either[L, RR]): Either[L, RR] = either match {
    case Left(l) => Left(l)
    case Right(r) => f(r)
  }
  def >>=[RR](f: R => Either[L, RR]) = flatMap(f)
}