CODEWITHSUNDEEP
prolog
rphello101
rphello101

Reputation: 1771

Prolog and sibling relationship?

I'm new to Prolog and having a bit of difficulty. I have:

man(ken).
man(tom).
woman(juli).

father(ken, tom).
father(ken, juli).

male(A) :- man(A).
brother(A,B) :- male(A), father(C,A), father(C,B), (A \= B).

I know the male/man is redundant, but it's part of the assignment. Anyway, when I try something like: 

|?- brother(tom, juli).

I get "no" as the response. I'm sure I've made a stupid, simple mistake, but my lack of understanding is making it very hard to find. Can anyone see what my problem is?

Upvotes: 1

Views: 316

Answers (1)

lurker
lurker

Reputation: 58244

When you enter:

|?- brother(tom, juli).

You'll see a response something like this (SWI Prolog):

true ? ;

no
| ?-

So it first responds with "true" (gives a match) and then, after you enter ; to show more solutions, it says "no" to indicate there are no further solutions. Some prolog interpreters may say "no" or "false" in this case, with the same meaning. This response from the prolog interpreters initially throws many a new prolog user.

You could, alternatively, press "enter" which just means you're done and don't want to see any further solutions:

true ?

yes
| ?-

Then you get "yes".

Upvotes: 3

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