[ghc-steering-committee] #380 GHC2021: Let's deprecate ExistentialQuantification

Richard Eisenberg rae at richarde.dev
Fri Dec 4 14:34:11 UTC 2020

I do use the data Ex = forall a. ... syntax occasionally, but only when I'm emphasizing that I'm not building a GADT. I would entertain the thought of removing it. Yet, I don't think we can do so as part of this process, as we don't have a combination of extensions that allows GADT-syntax existentials but not this other syntax. (Even -XGADTs -XNoExistentialQuantification doesn't eliminate it.)

In any case, I've voted against GADTs, and so if you want to disentangle this one piece of syntax, that would also be a vote against GADTs, followed up with a proposal to spin out this syntax into its own extension.


> On Dec 4, 2020, at 9:14 AM, Spiwack, Arnaud <arnaud.spiwack at tweag.io> wrote:
> Ah one clarification, GADTSyntax alone does not enable existential types. You need to enable either ExistentialQuantification or full GADTs.
> It makes more than perfect sense, but I wasn't aware of this. A consequence of always enabling -XGADTs, I suppose :-) .
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