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

[Iavor Diatchki]

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> 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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