How to write a Prolog program

Question

I don't know how to write a Prolog program for the following scenario.

1. If any two person having same hobby then  they like each other.
2. Every gardener likes the Sun.

I did this but I don't know whether it is correct or not.

like(gardener,sun).

Please help me to solve it.

Will Ness Will Ness · Accepted Answer · 2018-09-20T15:27:04

Prolog rules follow the "reversed-IF" template:

Head :- Goal1, ..., GoalN.

means (roughly), "Head holds if Goal1, ..., GoalN all hold".

Put the other way around it means, "if Goal1, ..., GoalN all hold, then Head also holds".

This fits exactly your first sentence, thus it can be encoded as a rule:

likes(A, B) :-                   % Head :-
    hobby( A, HobbyA),           %   Goal1,
    hobby( B, HobbyB),           %   Goal2,
    same( HobbyA, HobbyB),       %   Goal3,
    dif( A, B).                  %   Goal4.
    % different persons, not the same one

The second sentence too fits the same template:

likes(A, sun) :-
    isA(A, gardner).

With the most natural encoding of isA( X, Y) as simply a unification X = Y, this becomes equivalent to the fact that you wrote. Facts are rules with no body.

How to write a Prolog program

1 Answers