[m-users.] Mode selection

Michael Richter ttmrichter at gmail.com
Thu Oct 16 13:39:23 AEDT 2014

Documenting something as fundamental as the selection algorithm used deep
in compiler internals or on an ephemeral construct like a mailing list
seems a bit whimsical.  Does this not belong in the reference manual under
the modes chapter?

On 16 October 2014 09:33, Julien Fischer <jfischer at opturion.com> wrote:

> On Thu, 16 Oct 2014, Paul Bone wrote:
>> This question came up on IRC today.  Consider append/3:
>>    :- pred append(list(T), list(T), list(T)).
>>    :- mode append(in, in, out) is det.
>>    :- mode append(out, out, in) is multi.
>> And a call to append with each of it's arguments fully instantiated.
>>    % I've written these out so that I can name them and refer to them
>>    % below.
>>    A = [1, 2],
>>    B = [3],
>>    C = [1, 2, 3],
>>    append(A, B, C).
>> This is a case where "append(in, in, in) is semidet" is an implied mode.
>> While it makes no (declarative semantics) difference, which mode of append
>> will be used here?  Does the compiler select the first mode that fits or
>> the
>> "best" mode?
>> A follow up question.  What if the implied mode is written down in the
>> declaration.
> See the comment above the predicate choose_best_match/8 in
> compiler/modecheck_call.m.  It describes the selection algorithm used.
> Or indeed just see the mailing list archives, as this question has
> been asked (and answered!) before.
> Cheers,
> Julien.
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