% Quicksort implementation in IF/Prolog
quicksort([], []).
quicksort([H|T], Sorted) :-
    partition(H, T, Less, Greater),
    quicksort(Less, SortedLess),
    quicksort(Greater, SortedGreater),
    append(SortedLess, [H|SortedGreater], Sorted).

partition(_, [], [], []).
partition(Pivot, [H|T], [H|Less], Greater) :-
    H =< Pivot, !,
    partition(Pivot, T, Less, Greater).
partition(Pivot, [H|T], Less, [H|Greater]) :-
    H > Pivot,
    partition(Pivot, T, Less, Greater).

:- quicksort([3, 1, 4, 1, 5, 9, 2, 6, 5, 3], Sorted),
   write(Sorted), nl.