Re: [ghc-steering-committee] #371: Stop treating ~ magically. Rec: weak accept

I'm still not sure what problem this proposal solves. The proposal alludes to some code simplification but doesn't give me a good idea of how much simpler this would make the code. Also note that -XGADT becomes mostly vacuous with this proposal: -XGADTSyntax + -XExistentialTypes imply GADTs (both are in -XGHC2021). Not that I mind, really, I actually probably prefer it this way. But it's worthy of notice. On Thu, Apr 22, 2021 at 4:10 AM Richard Eisenberg wrote:

Hi committee,

This proposal has been updated to include exporting (~) from the Prelude. This means that migration is much easier than it was previously, likely not requiring any import changes (or just in a project's custom Prelude). Users will have to enable -XTypeOperators (and could choose to disable -XGADTs or -XTypeFamilies). With this new export, I'm more firmly in favor of cleaning up this one little corner: let's accept.

I will wait one week for any comments, and then will accept this proposal.

Thanks, Richard

On Apr 1, 2021, at 2:37 PM, Richard Eisenberg wrote:

On Apr 1, 2021, at 3:59 AM, Vladislav Zavialov (int-index) < vlad.z.4096@gmail.com> wrote:

Exporting from Prelude is not a panacea: without a compatibility fallback, users of custom preludes will be affected. The proposed migration story means that for 8 releases, no existing code will break at all.

Right. I wasn't suggesting a change to the migration plan -- just that (~) would additionally be exported from the Prelude. The warning would trigger only when (~) isn't in scope, meaning that many users won't need to react to this change (given that -XTypeOperators is now on by default).

As for the specialness of ~: yes, it's special, but we export other special things from the Prelude, like $ (which automatically enables -XImpredicativeTypes).

On Apr 1, 2021, at 9:59 AM, Alejandro Serrano Mena wrote:

I meant the usual convention that type constructors must start with a capital letter or the : symbol. But in this case I had forgotten that with TypeOperators on, those conventions behave differently for types than for terms.

This used to be true, but the requirement that the first letter be a capital letter or : was dropped some time ago -- before I started using Haskell, in any case. It is independent of -XTypeOperators, which is necessary for any infix type level syntax.

But those custom preludes would have to be updated anyway, right?

Yes, they would.

Richard _______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee

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