How to use the 'Univ' ( =../2 ) prolog predicate with a Logtalk object method as parameter ?
Consider this code :
baz(foo(X)) :-
write(predicate), write(X), nl.
run :-
Term =.. [baz, foo(testfoo)],
write(Term), nl, Term,nl,
TermLgt =.. [bar::baz, foo(testfoo2)],
write(TermLgt), nl, Term,nl.
:- object(bar).
:- public(baz/1).
baz(foo(X)) :-
write(method), write(X), nl.
:- end_object.
:- object(main).
:- public(run/0).
run :-
Term =.. [baz, foo(testfoo)],
write(Term), nl, Term,nl,
TermLgt =.. [bar::baz, foo(testfoo2)],
write(TermLgt), nl, Term,nl.
:- end_object.
I'll obtain :
?- {myfile}.
% (0 warnings)
true.
?- run.
baz(foo(testfoo))
predicatetestfoo
ERROR: =../2: Type error: `atom' expected, found `bar::baz' (a compound)
?- main::run.
baz(foo(testfoo))
ERROR: Undefined procedure: baz/1
ERROR: However, there are definitions for:
ERROR: baz/1
What workaround to use for a good interpretation / compilation ? It seems issue is the same with swi-prolog building predicate like predsort/3 (predsort/3 doc).
The standard =../2 predicate expects, when constructing a term from a list, that the first list argument be an atom but bar::baz is a compound term with functor ::/2 (which is both defined as a predicate - for top-level queries - and as an operator when Logtalk is loaded). The solution is to write instead:
baz(foo(X)) :-
write(predicate), write(X), nl.
run :-
Term =.. [baz, foo(testfoo)],
write(Term), nl, call(Term), nl,
TermLgt =.. [::, bar, Term],
write(TermLgt), nl, call(Term), nl.
:- object(bar).
:- public(baz/1).
baz(foo(X)) :-
write(method), write(X), nl.
:- end_object.
:- object(main).
:- public(run/0).
run :-
Term =.. [baz, foo(testfoo)],
write(Term), nl, Term,nl,
TermLgt =.. [::, bar, Term],
write(TermLgt), nl, Term,nl.
:- end_object.
With this changes, you get:
?- {univ}.
% [ /Users/pmoura/Desktop/univ.lgt loaded ]
% (0 warnings)
true.
?- run.
baz(foo(testfoo))
predicatetestfoo
bar::baz(foo(testfoo))
predicatetestfoo
true.