[ghc-steering-committee] a plea for PolyKinds

[Richard Eisenberg]

The truth is that (Type :: Type) is true no matter what (though you'd need KindSignatures for GHC to accept that). The features that were previously -XTypeInType have been moved into -XPolyKinds (and a few in -XDataKinds), because there seemed to be very little reason to keep the two extensions separate. PolyKinds essentially allows two things: it allows users to write variables and other constructs (like `forall`) in kinds, and it allows GHC to do kind-generalization. But nothing about -XPolyKinds really changes the relationship between types and kinds.

Richard

> On Dec 3, 2020, at 2:53 PM, Iavor Diatchki <iavor.diatchki at gmail.com> wrote:
> 
> Oh?  Perhaps I am confused, if we can have PolyKinds without TypeInType, I'd be happy to change my vote.  My understanding was that basically `TypeInType` got renamed to  `PolyKinds` but I might be confused.
> 
> -Iavor
> 
> On Thu, Dec 3, 2020 at 11:50 AM Alejandro Serrano Mena <trupill at gmail.com <mailto:trupill at gmail.com>> wrote:
> But PolyKinds does not require TypeInType, according to the docs [https://downloads.haskell.org/ghc/latest/docs/html/users_guide/glasgow_exts.html#extension-PolyKinds <https://downloads.haskell.org/ghc/latest/docs/html/users_guide/glasgow_exts.html#extension-PolyKinds>] it is in fact the other way around: TypeInType implies PolyKinds. Of course, the fact that kinds and types are unified may leak somehow, but I have a hard time figuring out an example of such.
> 
> El jue, 3 dic 2020 a las 18:51, Iavor Diatchki (<iavor.diatchki at gmail.com <mailto:iavor.diatchki at gmail.com>>) escribió:
> I would totally support that if PolyKinds was implemented without requiring TypeInType, but with the current design for me this is a solid `no`.
> 
> 
> On Thu, Dec 3, 2020 at 9:48 AM Joachim Breitner <mail at joachim-breitner.de <mailto:mail at joachim-breitner.de>> wrote:
> Hi,
> 
> Am Donnerstag, den 03.12.2020, 16:40 +0000 schrieb Richard Eisenberg:
> > Vote for PolyKinds!
> 
> convinced.
> 
> Cheers,
> Joachim
> -- 
> Joachim Breitner
>   mail at joachim-breitner.de <mailto:mail at joachim-breitner.de>
>   http://www.joachim-breitner.de/ <http://www.joachim-breitner.de/>
> 
> 
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