[ghc-steering-committee] Proposal #556 recommendation: accept

[Simon Peyton Jones]

I concur!

Simon

On Thu, 2 Feb 2023 at 12:40, Richard Eisenberg <lists at richarde.dev> wrote:

> Hi all,
>
> Vlad has proposed https://github.com/ghc-proposals/ghc-proposals/pull/556,
> an amendment to recently accepted proposal #448 on scoped type variables.
> It adds a nuance saying that
>
>   f (MkT @(a :: <<here>>)) = ...
>
> should have the same scoping behavior as
>
>   f (MkT (x :: <<here>>)) = ...
>
> Note that the first is a kind signature of a
> visible-type-application-in-a-pattern, while the second is a pattern
> signature. The intended scoping rule says that the use of an in-scope type
> variable in these positions is an occurrence, while the use of an
> out-of-scope type variable brings that variable into scope. Vlad's proposal
> corrects the phrasing in the original proposal that aligns the treatment of
> the kind signature with the type it is describing, forbidding e.g. the use
> of a repeated variable in the kind signature.
>
> Vlad's amendment makes the proposal what I had intended when I wrote #448;
> I strongly recommend acceptance.
>
> I think this is a small tweak of a technical detail buried in #448 and
> hope this does not cause widespread debate. I will accept this proposal in
> a week if I don't hear objections.
>
> Thanks!
> Richard
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