Re: Ann: SWI-Prolog 6.5.1

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.


-- 
Abramo Bagnara

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