Find the divisors of a number using Prolog by using recursion

I want to print the divisors of a number in Prolog and I have made the following code:

find_and_display_divisors(N) :-
    write('Divisors of '), write(N), write(':'), nl,
    find_divisors(N, 1).

find_divisors(N, D) :-
    D =< N,
    0 is N mod D,
    write(D), write(' '),
    NextD is D + 1,
    find_divisors(N, NextD).
find_divisors(_, _).

The problem that I have is that when I call my program with find_and_display_divisors(8), it only prints 1 2 true; however, it is missing the other values like 4 and 8. What am I missing?

Solution

When a number is not a divisor, you still need to go to next step. find_divisors(_, _) just stops the iteration at the first non-divisor.

So you will need a new clause covering the non-divisor part.

find_divisors(N, D) :-
    D =< N,
    M is N mod D,
    M > 0,
    NextD is D + 1,
    find_divisors(N, NextD).

You might want to include this if you want the predicate to succeed.

find_divisors(N, D) :- N < D.

PS: TA_intern's answer is idiomatic way to do it. Decouple side effects from logic code as much as possible.

Full working code:

find_and_display_divisors(N) :-
    write('Divisors of '), write(N), write(':'), nl,
    find_divisors(N, 1).

find_divisors(N, D) :-
    D =< N,
    0 is N mod D,
    write(D), write(' '),
    NextD is D + 1,
    find_divisors(N, NextD).

find_divisors(N, D) :-
    D =< N,
    M is N mod D, M > 0,
    NextD is D + 1,
    find_divisors(N, NextD).

find_divisors(N, D) :- N < D. % you can ignore this if you just need to print