Non-blocking serial execution of futures

serialFutures.scala

// see http://www.michaelpollmeier.com/execute-scala-futures-in-serial-one-after-the-other-non-blocking/
def serialiseFutures[A, B](l: Iterable[A])(fn: A ⇒ Future[B])
  (implicit ec: ExecutionContext): Future[List[B]] =
  l.foldLeft(Future(List.empty[B])) {
    (previousFuture, next) ⇒
      for {
        previousResults ← previousFuture
        next ← fn(next)
      } yield previousResults :+ next
  }