Serially execute a list of futures, in Scala. I find myself writing this fairly often, typically for testing or debugging.

Serially.scala

object Serially {
  def apply[T, U](values: Seq[T])(body: T => Future[U])(implicit executionContext: ExecutionContext): Future[List[U]] =
    apply(values.toList)(body)

  def apply[T, U](values: List[T])(body: T => Future[U])(implicit executionContext: ExecutionContext): Future[List[U]] =
    values match {
      case Nil =>
        Future.successful(List.empty)
      case head :: tail =>
        body(head).flatMap(headResult =>
          apply(tail)(body).map(tailResult =>
            headResult :: tailResult))
    }
}