Question

Prolog has a unique way of handling things, especially since practically every operation involves recursion of one sort or another.

One of the classic examples every language has is sorting a list of integers into ascending order.

What is an optimal way (without using too many built-in predicates, which precludes a sort/2 predicate, of course) to sort a random list of integers?

Answer 1

Roman Barták’s Prolog Programming site gives examples of different sort algorithms, ending with an optimized quicksort.

quick_sort2(List,Sorted):-q_sort(List,[],Sorted).
q_sort([],Acc,Acc).
q_sort([H|T],Acc,Sorted):-
    pivoting(H,T,L1,L2),
    q_sort(L1,Acc,Sorted1),q_sort(L2,[H|Sorted1],Sorted)