An example of closures (or "nested predicates") in Prolog

closure_example.pl

 %Since SWI-Prolog does not have a built-in implementation of closures, I wrote my own implementation here.

:- initialization(main).
:- set_prolog_flag('double_quotes','chars').

main :- predicate_with_nested(1,C),writeln(C).

call_local(Definition,Params) :-
	copy_term(Definition,(Params :- Body)),
	call(Body).

predicate_with_nested(A,C) :-
	Closure = ((B,C1) :- C1 is B+A),
	A>0,
	call_local(Closure,(1,C)),
	call_local(Closure,(2,D)),
	writeln(D).