CODEWITHSUNDEEP
prolog
Afflatus
Afflatus

Reputation: 943

Prolog Rule for Fact with Structure

I have following facts in Prolog. symptom (A,B,C): symptom A in region B can be caused by virus C (abbreviation, full name)

symptom(delirium,mind,virus(rbs, rabies)).
symptom(delirium,mind,virus(tbe, tick-borne-encephalitis)).
symptom(discomfort,mind,virus(rbs, rabies)).
...

I want to ask what type of viruses can for example cause a specific symptom. For this I want to declare a rule 'causedBy(X,Y)' where in query I could send the symptom and it gives me the list of possible viruses.

The question is how can I just send the symptom and get the list of only abbreviations of possible viruses?

Upvotes: 1

Views: 775

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726809

You can do it like this:

causedBy(X,Y) :- symptom(X, _, virus(Y, _)).

(demo in SWI Prolog on ideone).

The process of unification is recursive, you can nest names as deeply as you need for unifying with your facts. In this case, virus(Y, _) is nested inside symptom/3 call to "extract" only the first element of the virus pair.

Upvotes: 1

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