Comparing a variable and a predicate in Prolog

Question

I want to check if a variable, say X, is a predicate of the form add( ). How do I check if this is true? X == add( ) does not work, neither does X is add(_). How can I achieve this comparison?

Answer 1

The general, generic way to do so is:

Specific = add(_), ..., subsumes_term(add(_Any), Specific).

Often, people will optimize this to:

Specific = add(_), ..., nonvar(Specific), Specific = add(_).

But in the general case, you will need subsumes_term/2