Re: [ghc-steering-committee] #380 GHC2021: Current status

arnaud would miss: Arrows, ExplicitNamespaces, ForeignFunctionInterface, FunctionalDependencies, GADTs, MonadFailDesugaring, MonoLocalBinds, PartialTypeSignatures, StarIsType, TypeFamilyDependencies

Of these 10 extensions. Let me note that - ForeignFunctionInterface is part of Haskell 2010 - MonadFailDesugaring is the current default of GHC - MonoLocalBinds is implied by TypeFamilies, which is otherwise included So I assume that these are things which we've forgotten, rather than things that we oppose. On Fri, Dec 4, 2020 at 9:22 AM Spiwack, Arnaud wrote:

On Thu, Dec 3, 2020 at 6:31 PM Richard Eisenberg wrote:

...

The problem I described would arise when someone who does not know about GADTs and type inference accidentally writes a GADT. But this cannot happen easily today, precisely because of the need to write the extension.

Useful, popular, and stable all help argue for an extension (and I agree here!), but I'm more concerned about error messages and the beginner experience, captured in our Criterion 2 of https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0372-gh... .

This is not a very believable objection in my opinion. GADTs are guarded by a different syntax which isn't used by someone who doesn't know about GADTs. So writing a GADT by accident is exceedingly unlikely. Besides, Ocaml has GADTs by default (with a similar syntax split as Haskell's). I don't believe I've ever heard anybody complain about GADTs since they've landed, certainly of anybody writing one by mistake.