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

Spiwack, Arnaud arnaud.spiwack at tweag.io
Fri Dec 4 08:31:24 UTC 2020

>    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 <arnaud.spiwack at tweag.io>

> On Thu, Dec 3, 2020 at 6:31 PM Richard Eisenberg <rae at richarde.dev> 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-ghc-extensions.rst#criteria
>> .
> 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.
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