let r_quicksort l =
    let split list pivot =
      let rec _split inf sup = function
        | [] -> (inf, sup)
        | h :: t ->
          if h < pivot then _split (h :: inf) sup t
          else              _split inf (h :: sup) t
      in _split [] [] list
    in

    let rec sort result = function
      | [] -> result
      | [a] -> a :: result
      | pivot :: t -> let (inf, sup) = split t pivot in sort (pivot :: (sort result inf)) sup

    in List.rev (sort [] l)
    ;;