Re: [ghc-steering-committee] #547: Remove kind constraints, Recommendation: accept

I'm not extremely worried about removing equality constraints in kinds themselves, but I am slightly worried that this proposal will unexpectedly prevent (existing) uses of GADTs with DataKinds. If I understand correctly, this version of MkT will be usable in types: data T a where MkT :: Bool -> T Bool but this will not (even though it could be rewritten to the former): data T a where MkT :: a ~ Bool => Bool -> T a Moreover, this MkT not be usable in types at all: type family F a data T a where MkT :: F a ~ Bool => Bool -> T a I suppose we can live with this in exchange for the gain in simplicity, especially as there seems to be agreement that maintaining the feature is simply too costly. But I would not be all that surprised if some users' code breaks as a result. Cheers, Adam On 21/11/2022 08:32, Arnaud Spiwack wrote:

Not many opined. Unless there is opposition, I'll mark the proposal as acceptable sometime before the end of the week.

On Thu, 17 Nov 2022 at 11:20, Arnaud Spiwack mailto:arnaud.spiwack@tweag.io> wrote:

> authored by Richard and Simon, and double-checked by Arnaud, I’m happy > to concur.

😀

To clarify: the main question is whether we are confident that it won't break too many users. I don't have divination powers that make my word particularly trustworthy on this point. Yet, I do feel pretty confident.

On Mon, 14 Nov 2022 at 12:51, Joachim Breitner mailto:mail@joachim-breitner.de> wrote:

Hi,

Am Montag, dem 14.11.2022 um 11:28 +0100 schrieb Arnaud Spiwack: > I recommend acceptance.

authored by Richard and Simon, and double-checked by Arnaud, I’m happy to concur.

Cheers, Joachim https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee

-- Adam Gundry, Haskell Consultant Well-Typed LLP, https://www.well-typed.com/ Registered in England & Wales, OC335890 27 Old Gloucester Street, London WC1N 3AX, England