[ghc-steering-committee] Modern Scoped Type Variables #448: recommendation (mostly) accept

[Simon Marlow]

In the spirit of not accepting proposals that lead to language forks, it
would be great to get some clarification on the concerns that Arnaud raises
here:

On Tue, 29 Mar 2022 at 16:02, Spiwack, Arnaud <arnaud.spiwack at tweag.io>
wrote:

> With the caveat that this proposal introduces quite a few extensions. And
> at this point, I'm still not quite sure what Richard recommends is the set
> of extensions that I should use (and I'm slightly dismayed that I believe
> that it will be a set of cardinal more than 1). I think this reflects a
> vision of extensions as switches to customise the behaviour of GHC. This
> vision, as I've stated before, is very alien to me: I see extensions as
> staging areas for features to become an integral part of Haskell. So I
> don't know what to think of all these extensions. I'm definitely not
> against splitting -XScopedTypeVariables into smaller components, if it is
> done so that they are reassembled in a different way in an alternative
> extension that would now be the recommended default (or at least is to
> become the next recommended default).
>

I think we should express an opinion about the intended direction. Are we
advising that ExtendedForallScope is a dead end, because we want
TypeAbstraction?

Cheers
Simon



>
> Finally, there are Sections 6 to 8. These are entirely new. Though they
> are working towards the new principles (well, as far as I can tell, Section
> 6 doesn't contribute to the principles, but it is a stepping stone for both
> Sections 7 and 8). These sections are concerned with adding local
> let-bindings of type variables, in particular inside types and patterns.
>
> By the way, Section 7 proposes two syntaxes for let binders in patterns,
> and I  *strongly* prefer the second syntax, which reads something like `f
> (let b = Bool) (True :: Bool) = …`.
>
> Anyway, these are new, I feel that they are a bit out of place in a
> proposal that is about tidying up the existing designs. That being said,
> they are here, and they seem like fairly uncontroversial to me, (except,
> probably the syntax `(let b = _)` to bind a variable to a type to be filled
> by the compiler). I'm fine with accepting these, though they may require a
> bit more scrutiny than the rest.
>
> Best,
> Arnaud
>
> _______________________________________________
> ghc-steering-committee mailing list
> ghc-steering-committee at haskell.org
> https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/ghc-steering-committee/attachments/20220401/b6e48d37/attachment.html>