Re: Ann: SWI-Prolog 6.5.1

Il 13/08/2013 10:29, Abramo Bagnara ha scritto:
> Il 12/08/2013 22:43, Jan Wielemaker ha scritto:
>> Hi,
>>
>> I've uploaded SWI-Prolog 6.5.1.  There are a lot of changes.  Highlights:
>>
>>   - Detection of `semantic singletons' by the compiler.  This proofs
>>     to result in a quite high percentage of real bugs.  My rough
>>     estimate is about 1/3th!  And this is on established code!
> 
> The added warnings are indeed wonderful and *very* useful to spot bugs.
> 
> Still I have some problems to write warning free code in presence of
> term expansion and conditional term expansion:
> 
> %flag :- fail.
> flag.
> 
> :- if(flag).
> term_expansion((:- f(A)), f(A, A)).
> :- else.
> term_expansion((:- f(_A)), []).
> :- endif.
> 
> :- f(A).
> :- f(_A).
> 
> Warning: /home/abramo/z.pl:10:
> 	Singleton variables: [A]
> Warning: /home/abramo/z.pl:11:
> 	Singleton-marked variable appears more than once: _A
> 
> Do I have a way to write :- f(A) (so to have warning from the expansion
> with singleton variables when flag is true) and to avoid warning when
> flag is false?
> 
> The other way is to write :- f(_A) and to use style_check inside the
> expansion, but in this case I'd lose the warning from the expansion.
> 

A similar issue comes from the following:

goal_expansion(nofail(G),
               (G *->
                   true
               ;
                   print_message(error, assumption_failed(G)),
                   trace,
                   G
               )).

f1(In) :-
    nofail(p(In, _Out)).

f2(In) :-
    nofail(p(In, Out)).

f3(In) :-
    nofail(p(In, _)).


Both f1 and f2 gives warnings, f3 does not give any warnings, but asks
to me to reduce code readability.


-- 
Abramo Bagnara

Via Borghesi, 16
48014 Castel Bolognese (RA) - Italy