Re: Ann: SWI-Prolog 6.5.1

Il 13/08/2013 12:07, Jan Wielemaker ha scritto:
> On 08/13/2013 10:59 AM, Abramo Bagnara wrote:
>> 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.
> 
> Yes.  That is a fairly realistic example.  To be honest, I don't know
> what to do about it.  The alternative is to do all this purely at the
> syntactic level, but that things such as below won't do the job
> correctly (comes from SICStus compatibility layer).
> 
>     goal_expansion(if(If,Then,Else), (If *-> Then; Else)).
> 
> I started this at the compiler level for two reasons:
> 
>   - To make cases as the if/3 above work
>   - The compiler has to analyse the variable status anyway, so
>     doing it from there avoids duplicate work.
> 
> Here is a case where you want to do the analysis prior to expansion :-(
> 
> Of course, we could make the variable analysis of the compiler
> available as a separate functionality and use it before goal/term
> expansion on the input.
> 
> An alternative is to stop complaining about _X being used multiple
> times.  That would be really easy.

What do you think about to exclude only __Var from this check (note the
double underscore)?


-- 
Abramo Bagnara

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