[m-rev.] for review: provide alternatives to can-fail functions in the library

[Zoltan Somogyi]

On Fri, 9 Aug 2024 11:44:35 +1000, Julien Fischer <jfischer at opturion.com> wrote:
> > This diff also adds some "XXX STATEVAR"s to library/injection.m.
> > The marked predicates have non-statevar-friendly argument orders.
> > Given that injection.m is rarely used, I would like to simply change
> > those arguments orders in a follow-up diff, noting the change in NEWS.md.
> > Does anyone think that we need a more gradual implementation
> > of that change?
> 
> No, you can go ahead and change them.

Will do.

> > Something that would definitely have more impact is replacing the semidet
> > function in the enum typeclass. (The uenum typeclass already has a
> > semidet *predicate* in the same role.) Since you cannot obsolete one
> > typeclass method in favor of another, I can't think of a way to make any
> > changeover any less disruptive than just making the replacement and announcing it,
> > and expecting everyone to fix their instance declarations when they next update
> > their Mercury standard library. Can anyone else?
> 
> There are two sources of potential disruption:
> 
> 1. Users who have implemented their own instances of the enum typeclass; as you
> say they will just need to update.
> 
> 2. Users who have code that uses the from_int/1 method. For those, we can add
> the following to the enum module for the next release:
> 
>      :- pragma obsolete(func(from_int/1)).
>      :- func from_int(int) = T is semidet <= enum(T).
> 
> This can be deleted after the next release.

The attached diff does this. Since the concept has effectively been reviewed,
the diff is for post-commit review. What I am mainly seeking feedback on
is a new XXX in pred_table.m.

> The diff looks fine.

Thanks for the review.

Zoltan.



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