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

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. - Vlad

On 20 Feb 2021, at 14:34, Vitaly Bragilevsky 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...

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-mo...): %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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