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gbmele/closure_example.pl

Forked from jarble/closure_example.pl
Last active February 28, 2024 23:32
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An example of closures (or "nested predicates") in Prolog
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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).
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
:- op(1200, xfx, ==>).
:- op(1000, xfy, /\).
:- op(1100, xfy, \/).
term_expansion(A ==> B, B:- A).
goal_expansion(A /\ B, (A, B)).
goal_expansion(A \/ B, (A; B)).
man(X) /\ unmarried(X) ==> bachelor(X).
man(john).
man(peter).
unmarried(john).
main:-bachelor(X), writeln(X), nl, fail.
It yields an answer now:
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