[m-dev.] shims

[Julien Fischer]

On Mon, Sep 15, 2014 at 3:42 PM, Mark Brown <mark at mercurylang.org> wrote:

> On Mon, Sep 15, 2014 at 3:20 PM, Julien Fischer <jfischer at opturion.com>
> wrote:
> >
> >
> > On Fri, 12 Sep 2014, Peter Wang wrote:
> >
> >> On Thu, 11 Sep 2014 17:26:04 +1000, Peter Wang <novalazy at gmail.com>
> wrote:
> >>>
> >>>
> >>> Ideally you could update code immediately but maintain a fallback for
> >>> older libraries.  I don't think there is a way to do it currently, so
> >>> perhaps it is time for another pragma, e.g.
> >>>
> >>>     :- pragma shim(p/1, other.p/1).
> >>>
> >>>     p(X) :- ...
> >>
> >>
> >> This could not cope with predicates which just have their arguments
> >> reordered (hopefully a rare occurrence).
>
> If you require that other.p/1 not only exists, but has the same
> signature as p/1, then I think it will cope so long as the arguments
> don't have the same type.
>
> (If the signatures don't change, my proposal wouldn't cope either.)
>
> >
> >
> > Over the past few years it's been a very common occurrence in Mercury's
> > standard library.  (I'll grant that those reorderings were primarily
> > legacy issues and that APIs built against a current version of Mercury
> > are unlikely to have the same sort of problems.)
>
> In most of these cases the arguments have different types so the
> signature has changed, right?
>

Pretty much.

Cheers,
Julien.
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