Illustrated here is a program written in the logical language of Prolog.
This particular program defines a series of rules that will sort a list. It illustrates how a logical language can be used for more conventional algorithms like list sorting. Lets take a closer look at the code.
permute([], []). permute(L, [H|T]) :- remove(H, L, R), permute(R,T). remove(X, [X|T], T). remove(X, [H|T], [H|NT]) :- remove(X,T,NT). sorted([]). sorted([_]). sorted([X,Y|T]) :- X =< Y, sorted([Y|T]). sortlist(List, Sorted) :- permute(List, Sorted), sorted(Sorted).
Here is an example input and output:
1 ?- sortlist([1,5,4],X). X = [1, 4, 5] .
The output demonstrates that the provided list is sorted according to ascending order.