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

While the use of (~) itself no longer requires -XGADTs, the usual desugaring of GADTs still does. So this will require the extension: data G a where MkG :: G Int even though this will not: data T a where MkT :: (a~Int) => T a Perhaps that is what you meant by ‘vacuous’, but I wouldn’t go as far as to say that -XGADTs becomes implied by -XGADTSyntax and -XExistentialTypes. - Vlad

On 22 Apr 2021, at 12:25, Spiwack, Arnaud wrote:

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.

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