FutureOption.scala

case class FutureOption[A](value: Future[Option[A]])

type HttpRoutes = Http[FutureOption]

object HttpRoutes {
  def of(pf: PartialFunction[Request, Future[Response]]): HttpRoutes =
    Kleisli(req => FutureOption(pf.lift(req).sequence))
}

implicit val monadForFutureOption: Monad[FutureOption] = 
  new Monad[FutureOption] with StackSafeMonad[FutureOption] {
    def pure[A](x: A) = FutureOption(Future.successful(Some(x)))
    def flatMap[A, B](fa: FutureOption[A])(f: A => FutureOption[B]): FutureOption[B] = {
      FutureOption(fa.value.flatMap {
        case Some(a) => f(a).value
        case None => Future.successful(None) 
      })
    }
  }