Vanilla Scala exercise

vanilla-scala.scala

import scala.concurrent._
import scala.concurrent.duration._
import scala.concurrent.ExecutionContext.Implicits.global

def getInteger(x: Int) = Future.successful(
  if (x == 11) None else Some(x))

def sequence[T](l: Seq[Option[T]]): Option[List[T]] = l.foldRight(Some(Nil) : Option[List[T]]) {
  (or, ox) => for (r <- or; x <- ox) yield (r :: x)
}

def computeList(n: Int): Future[Option[List[Int]]] =
  Future.sequence((1 to n).map(getInteger)).map(sequence)

computeList(3) // will result in List(1, 2, 3)