EitherUtils.scala

object EitherUtils {

  implicit class EitherWithFilter[L, R](either: Either[L, R]) {
    def withFilter(filter: R => Boolean): Either[L, R] = either.flatMap { rv =>
      try {
        if (filter(rv)) Right(rv) else throw new RuntimeException("withFilter returned false")
      } catch {
        case e: EitherException[_] => Left(e.value.asInstanceOf[L])
      }
    }
  }

  case class EitherCondition(condition: Boolean) {
    def thenFailWith[T](error: => T): Boolean =
      if (condition) throw new EitherException[T](error)
      else true
  }

  private[EitherUtils] case class EitherException[T] (value: T) extends RuntimeException with NoStackTrace


  implicit def toDataCondition(cond: Boolean): EitherCondition = EitherCondition(cond)
}