Question

Is it possible to have a “variable arity predicate” in Prolog?

I mean something like this:

my_predicate( [a,b,c], [a,c], [a], [a,b,c,d], N, RESULT)

with the number of initial lists unknown at the beginning?

Using the univ operator ( =.. ) it would be possible to unify it with a list of terms and traversing it like every other list. But how to write the goal?

my_predicate(??) =.. [??]

I really don’t know if this is even possible..

Answer 1

you can define predicates with different arities that have the same name but they will be different predicates.

foo(1).
foo(2,1).

?-foo(2).
false

my suggestion is to change the encoding; instead of a number of initial lists, have a list of initial lists.
the other solution would be to write predicates for all the possible numbers of arguments (or dynamically generate them).