MT.scala

object MyApp{
  trait ApplicativeFunctor[A, F[A]] {
    def apply[X](a:X): F[X]
    def map[B](f: A => B): F[B]
  }

  trait Monad[A, M[A]] extends ApplicativeFunctor[A, M] {
    def flatMMap[B](f: A => M[B]): M[B]
  }


  class OptionT[A, M[A]] (m:ApplicativeFunctor[Option[A], M]) extends ApplicativeFunctor[A, ({type T[X]=M[Option[X]]})#T] {
    override def apply[X](a:X): M[Option[X]] = m(Option(a))
    override def map[B](f: A => B): M[Option[B]] =
      m map {(x: Option[A]) => x map f}
  }

  class OptionTM[A, M[A]](m:Monad[Option[A], M]) extends OptionT[A, M](m) with Monad[A, ({type T[X]=M[Option[X]]})#T] {
    override def flatMMap [B] (f:A => M[Option[B]]) : M[Option[B]] =
      m flatMMap {
        case Some(z) => f(z)
        case None => m(None)
      }
  }

  abstract class MyTest{

    import scala.concurrent.Future
    import scala.concurrent.ExecutionContext.Implicits._

    // The unchanged future monad, but applied to Option[A]
    class FutureOM[A](fut: Future[Option[A]]) extends Monad[Option[A], Future] {
      def apply[X](a:X): Future[X] = Future { a }
      def map[B](f: Option[A] => B): Future[B] = fut map f
      def flatMMap[B](f: Option[A] => Future[B]): Future[B] = fut flatMap f
    }

    implicit def optionMF[A](f:Future[Option[A]]) = new OptionTM(new FutureOM(f))


    trait FooService {
      def find(id: Int): Future[Option[Int]]
    }

    trait BarService {
      def find(id: Int): Future[Option[Int]]
    }

    trait QuuxService {
      def find(id:Int): Future[Option[Int]]
    }

    val fooService: FooService
    val barService: BarService
    val quuxService: QuuxService

    def finalRes(): Future[Option[Int]] =
      fooService.find(1) flatMMap (barService.find _) flatMMap (quuxService.find _)
  }

}