[ghc-steering-committee] [Proposal] #193: Make `forall` a keyword in type (recommendation: accept)

[Eric Seidel]

Yep, it's been at least a week and the feedback has been all positive.

I'll mark the proposal accepted.

On Thu, Feb 14, 2019, at 12:54, Simon Peyton Jones wrote:
> Shall we conclude on this?  Vlad has implemented it:
> https://gitlab.haskell.org/ghc/ghc/merge_requests/363
> 
> Simon
> 
> From: ghc-steering-committee <ghc-steering-committee-
> bounces at haskell.org> On Behalf Of Iavor Diatchki
> Sent: 06 February 2019 01:04
> To: Eric Seidel <eric at seidel.io>
> Cc: ghc-steering-committee <ghc-steering-committee at haskell.org>
> Subject: Re: [ghc-steering-committee] [Proposal] #193: Make `forall` a 
> keyword in type (recommendation: accept)
> 
> Agreed that `forall` should be a keyword in types.   I didn't realize it 
> wasn't already :)
> 
> On Tue, Feb 5, 2019 at 4:51 PM Eric Seidel 
> <eric at seidel.io<mailto:eric at seidel.io>> wrote:
> This proposal suggests making `forall` a keyword at the type-level. 
> `forall` is currently only a keyword when `-XExplicitForAll` is enabled.
> 
> This change would avoid a potentially confusing situation where the 
> meaning of a type can change based on which extensions are enabled. For 
> example,
> 
> ```
> f2 :: forall a -> a -> a
> ```
> 
> with no extensions, the `forall a` would be interpreted as two regular 
> type variables. But if we enable the upcoming "visible dependent 
> quantification" extension (I assume there's an extension involved here 
> somewhere, the proposal doesn't say), the `forall a` would be 
> interpreted as a *single* dependently quantified type variable `a`.
> 
> The only concerns are that this change could break existing programs, 
> and that it moves us further away from the standard. I'd be very 
> suspicious of any programs that used `forall` as a type variable, as 
> that's just ripe for confusion. And it's a very small step away from the 
> standard, so I don't think that should stand in the proposal's way 
> either.
> 
> I recommend we accept the proposal.
> 
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