Monad Transformers

gistfile1.scala

import scalaz._
import syntax.std.option._
import OptionT._
import scala.concurrent._
import scala.concurrent.duration._

import scala.concurrent.ExecutionContext.Implicits.global

val o1 = 1.some
val o2 = 2.some

val fo1: Future[Option[Int]] = Future.successful(o1)
val fo2: Future[Option[Int]] = Future.successful(o2)

val res1 = Await.result(fo1, 1.second)

val sum1F = for {
  intOpt1 <- fo1
  intOpt2 <- fo2
} yield {
  for {
    int1 <- intOpt1
    int2 <- intOpt2
  } yield int1 + int2
}

val sum1 = Await.result(sum1F, 1.second)

implicit val futureMonad: Monad[Future] = new Monad[Future] {
  override def point[A](a: => A): Future[A] = Future.successful(a)
  override def bind[A, B](fa: Future[A])(f: (A) => Future[B]): Future[B] = fa flatMap f
}

val sum2F: OptionT[Future, Int] = for {
  int1 <- optionT[Future](fo1)
  int2 <- optionT[Future](fo2)
} yield int1 + int2

val sum2 = Await.result(sum2F.run, 1.second)