Conditional Statements in Prolog

Question

I have just started prolog and was wondering if we can implement conditional statements like(if.else)in Prolog also and if so how?? Can someone implement this code in Prolog

Answer 1

One way to do it:

test(A) :-
    (   A =:= 2 ->
        write('A is 2')
    ;   A =:= 3 ->
        write('A is 3')
    ;   write('HAhahahahaah')
    ).

Another way to do it:

test(2) :-
    write('A is 2').
test(3) :-
    write('A is 3').
test(A) :-
    A \= 2, A \= 3,
    write('HAhahahahaah').

There are differences with these two codes, like choice points, behavior when A is not instantiated, and if A is treated as a number or not. But both will work the same way (except choice points left) and as expected with queries test(2)., test(3)., test(42).