MonadExample_Scala.scala

import scala.concurrent.{ Await, Future }
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.duration.DurationInt
 
def f(n: Int): Future[Int] = Future(n + 1)
def g(n: Int): Future[Int] = Future(n - 1)
def h(n: Int): Future[Int] = Future(n * 2)
 
val n = f(42).flatMap(g)
assert(Await.result(n, 1.second) == 42)
 
val m = for {
  m1 <- f(42)
  m2 <- g(m1)
  m3 <- h(m2)
} yield m3
assert(Await.result(m, 1.second) == 84)