class Loader[A,Marker](retrieve: Option[Marker] => Future[PagedResults[A,Marker]])(implicit ec:ExecutionContext){

  def foldUntil[B]( initial:B )( folder: (B, PagedResults[A,Marker]) => Future[(B,Boolean)], marker:Option[Marker] = None)(implicit         rc:RequestContext):Future[B] = {
    retrieve(marker).flatMap( results => {
      folder(initial,results).flatMap({ case (acc, finished) =>
        if (finished || !results.hasMore) Future successful acc
        else foldUntil(acc)(folder, results.marker)
      })
    })
  }

}