% example adopted from:
% Programming Language Prolog Part 2, Modules
% Committee Draft - January 14, 1998 X3J17/97/5
:- object(tracer).
:- info([
version is 2,
author is 'Paulo Moura',
date is 2000/7/24,
comment is 'Tracer for a goal call and exit ports.']).
:- public(trace/1).
:- metapredicate(trace(::)).
:- mode(trace(+callable), zero_or_more).
:- info(trace/1, [
comment is '.',
argnames is ['Goal']]).
trace(Goal) :-
write('call: '), writeq(Goal), nl,
call(Goal),
write('exit: '), writeq(Goal), nl.
write('fail: '), writeq(Goal), nl,
fail.
:- end_object.
