>>22 If you don't want Haskell, you can have this:
quicksort([], []).
quicksort([HEAD | TAIL], SORTED) :- partition(HEAD, TAIL, LEFT, RIGHT),
quicksort(LEFT, SORTEDL),
quicksort(RIGHT, SORTEDR),
append(SORTEDL, [HEAD | SORTEDR], SORTED).
partition(PIVOT, [], [], []).
partition(PIVOT, [HEAD | TAIL], [HEAD | LEFT], RIGHT) :- HEAD @=< PIVOT,
partition(PIVOT, TAIL, LEFT, RIGHT).
partition(PIVOT, [HEAD | TAIL], LEFT, [HEAD | RIGHT]) :- HEAD @> PIVOT,
partition(PIVOT, TAIL, LEFT, RIGHT).
append([], LIST, LIST).
append([HEAD | LIST1], LIST2, [HEAD | LIST3]) :- append(LIST1, LIST2, LIST3).