Post funny things about programming here! (Or just rant about your favourite programming language.)
something is a person if it is either Adam or Eve, or if it has a mother. We can express this in a single rule as follows:
person(X) :- (X=adam; X=eve; mother(X, Y)).
Can someone explain where the Y comes from? Is this something like, there exists a mother relation between this X and some Y?
mother can be used in several ways. If both X and Y variables are uninitialized, then it looks for all mother relationships. If one of them is initialized, it looks for matching relationships. If both are initialized, it returns true if such a relationship exists.
I learned Prolog in university and it was instructive. But has anyone ever professionally used it?
no
I'll admit I don't speak prolog but doesn't this definition lack a recursive case to ensure that the mother is either Eve or a descendent of Eve? And there should probably be a father case in there as well?
Depends on how you want to define your domain knowledge.
The thing you need to define for sure is the predicate mother/2 (Which has arity 2, or in other words, two arguments). From then on, multiple options are available:
mother(X, Y) as an "axiom", and define mother terms for all elements:mother(abel, eve).
mother(isaac, sarah).
mother(X, Y) from female(X) and parent(X, Y) terms.mother(X, Y) :-
parent(X, Y),
female(Y).
parent/2
terms instead of mother/2 and father/2.I never saw such a potent combination of gender politics and prolog
doesn’t this definition lack a recursive case to ensure that the mother is either Eve or a descendent of Eve
We don’t see the definition of mother. It might already encode that Y is a person.
And there should probably be a father case in there as well?
While every person does also have a father, it’s completely redundant, since being a person can fully be described by [Edit: ~~being~~ having] a mother (or being Adam or Eve).