[ghc-steering-committee] #390: Fine-grained pragmas, recommendation: accept

[Joachim Breitner]

Hi Vitaly,

what is the status of this? Richard said he supports acceptance, but I
am not sure if there are still open questions?

Cheers,
Joachim

Am Freitag, dem 23.07.2021 um 07:44 +0000 schrieb Alejandro Serrano
Mena:
>  Dear all,
> I’ve just updated the proposal following a great suggestion by Vlad.
> 
> Unfortunately, I don’t know enough about GHC’s parsing machinery to
> answer the question posed by Richard. I’ll repeat it in case somebody
> in the Committee can shed some light on it:
> 
> > The proposal use ; to separate the modifiers from the declarations.
> > Combined with the layout rule this allows us to write in two forms:
> > 
> > 
> > 
> >  > %NoTerminationCheck ; instance C Int where ...
> > 
> > 
> > > %NoTerminationCheck
> > > instance C Int where …
> > 
> > Would it be possible to allow the modifier to simply precede the
> > `instance` without turning the parser into a mess?
> > 
> 
> Regards,
> Alejandro
> 
> El 12 jul 2021 15:52:01, Richard Eisenberg <lists at richarde.dev>
> escribió:
>  
> > I'm happy with this updated proposal, though I've made a small
> > suggestion about making the ;s optional.
> > 
> > Regardless of whether this suggestion is taken, I support
> > acceptance.
> > 
> > Thanks,
> > Richard
> > 
> > > On Jul 4, 2021, at 5:12 AM, Vitaly Bragilevsky
> > > <bravit111 at gmail.com> wrote:
> > > 
> > > Dear Committee, 
> > > 
> > > I'm happy to repeat my recommendation to accept Alejandro's
> > > proposal which is now back from revision:
> > > Fine-grained pragmas for classes, families, and instances
> > > https://github.com/ghc-proposals/ghc-proposals/pull/390
> > > https://github.com/serras/ghc-proposals/blob/instance-pragmas/proposals/0000-fine-grained-undecidable.md
> > > 
> > > All the issues that arose in the previous discussion are now
> > > resolved. Does anyone have something to add? 
> > > 
> > > Vitaly
> > > 
> > > 
> > > 
> > > сб, 13 мар. 2021 г. в 12:38, Vitaly Bragilevsky
> > > <bravit111 at gmail.com>:
> > > > чт, 11 мар. 2021 г. в 16:31, Vladislav Zavialov (int-index)
> > > > <vlad.z.4096 at gmail.com>:
> > > > > I like the proposal and I would be happy to vote for its
> > > > > acceptance. However, it requires a little bit of polishing up
> > > > > with regards to its use of modifiers. In particular, it seems
> > > > > to treat modifiers as built-in units, whereas the core idea
> > > > > behind modifiers is that they are based on actual promoted
> > > > > types (with the exception of %1).
> > > > > 
> > > > > Hence it seems appropriate to send it back for revision until
> > > > > this point is addressed.
> > > > > 
> > > > 
> > > > 
> > > > Yes, I agree. There is also another issue. I think we need
> > > > either a deprecation story for UndecidableInstances, or a
> > > > statement that it should survive with some motivation behind
> > > > that. 
> > > > 
> > > > So, I'm sending this proposal back to Alejandro for review and
> > > > set the "needs revision" label on GitHub.
> > > > 
> > > > Vitaly 
> > > > > 
> > > > > - Vlad
> > > > > 
> > > > > > On 20 Feb 2021, at 14:34, Vitaly Bragilevsky
> > > > > <bravit111 at gmail.com> wrote:
> > > > > > 
> > > > > > Dear Committee,
> > > > > > 
> > > > > > Our own Alejandro has been proposed
> > > > > > Fine-grained pragmas for classes, families, and instances
> > > > > > https://github.com/ghc-proposals/ghc-proposals/pull/390
> > > > > > 
> > > > > https://github.com/serras/ghc-proposals/blob/instance-pragmas/proposals/0000-fine-grained-undecidable.md
> > > > > > 
> > > > > > His idea is to bring the flexibility of
> > > > > overlaps/overlapping/overlappable pragmas to termination
> > > > > checking, type inference, and constraint solving. Alejandro
> > > > > proposes to introduce the following %-modifiers (as in
> > > > > already
> > > > > accepted #370,
> > > > > https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0370-modifiers.rst
> > > > > ):
> > > > > > %NoTerminationCheck
> > > > > > %LiberalCoverage
> > > > > > %LiberalInjectivity
> > > > > > %Overlapping
> > > > > > %Overlappable
> > > > > > %Overlaps
> > > > > > to liberate conditions for classes and instances, type
> > > > > families, forall-types, etc. The first three modifiers can be
> > > > > used instead of the scary-sounding UndecidableInstances
> > > > > extension. The last three modifiers are supposed to be used
> > > > > instead of the  overlap*-pragmas for instances we already
> > > > > have.
> > > > > Note that this proposal doesn't suggest deprecating those
> > > > > extensions and pragmas.
> > > > > > 
> > > > > > I think that this proposal goes in the right direction and
> > > > > recommend accepting it.
> > > > > > 
> > > > > > As far as I understand, all the committee members,
> > > > > > including
> > > > > those with terms about to expire, have the right to either
> > > > > support this proposal or to raise a voice against it either
> > > > > here or at
> > > > > https://github.com/ghc-proposals/ghc-proposals/pull/390.
> > > > > > 
> > > > > > Regards,
> > > > > > Vitaly
> > > > > > 
> > > > > > 
> > > > > > 
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> > > > > > 
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> > > > > 
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-- 
Joachim Breitner
  mail at joachim-breitner.de
  http://www.joachim-breitner.de/