My quick sort

quick_sort.erl

-module(QS).
-export([quick_sort/1]).


quick_sort([]) -> [];
quick_sort([X]) -> [X];

quick_sort([X, Y]) ->
  if
    X =< Y -> [X, Y];
    X > Y -> [Y, X]
  end;

quick_sort(List) ->
  [Mid | _] = List,

  Left = lists:filter(fun(E) -> E < Mid end, List),
  Middle = lists:filter(fun(E) -> E == Mid end, List),
  Right = lists:filter(fun(E) -> E > Mid end, List),

  lists:append(lists:append(quick_sort(Left), Middle), quick_sort(Right)).