計算中と計算終了を表すコンテナ

gistfile1.scala

trait Container[+R, +C] {

  def map[A](f: C => A): Container[R, A]

  def flatMap[RR >: R, A](f: C => Container[RR, A]): Container[RR, A]

  def get[RR >: R](implicit ev: C <%< RR): RR

}
case class Calculating[+R, +C](element: C) extends Container[R, C] {

  def map[A](f: C => A): Container[R, A] = Calculating(f(element))

  def flatMap[RR >: R, A](f: C => Container[RR, A]): Container[RR, A] = f(element)

  def get[RR >: R](implicit ev: C <%< RR): RR = element

}
case class Result[+R](element: R) extends Container[R, Nothing] {

  def map[A](f: Nothing => A): Container[R, A] = this

  def flatMap[RR >: R, A](f: Nothing => Container[RR, A]): Container[RR, A] = this

  def get[RR >: R](implicit ev: Nothing <%< RR): RR = element

}