[mercury-users] Again: cc_ problem - what is Context requiring all solutions...

[Simon Taylor]

On 04-Sep-2001, Ondrej Bojar <oboj7042 at ss1000.ms.mff.cuni.cz> wrote:
> I got this error:
> 
> fstag.m:081: Error: call to predicate `fstag:cc_tagmap/2' with determinism
> `cc_nondet'
> fstag.m:081:   occurs in a context which requires all solutions.
> 
> And the context is:
> 
> :- mode my_something(in, out) is cc_multi.
> 
> my_something(In, MainOut) :-
>   (
>     cc_tagmap(In, TempOut),
>     % ... make TempOut into Out
>   ;
>     Out = ok(calculation_skipped_for_whatever_reason)
>   ),
>   % ... and perform further working on Out here to obtain MainOut...
>   % this futher part can never fail
> 
> It is fine for me, if cc_tagmap fails, it is fine, if it succeeds as well.
> I just do no want to backtrack it, because the ...making TempOut into Out
> is too expensive and all possible solutions of cc_tagmap are equal for
> this.
> 
> Why is cc_tagmap in a context requiring all solutions? It's embedded in
> my_something which is cc_ as well.

It's a bit hard to tell with most of the code missing.
Can "make TempOut into Out" fail?

Simon.
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