Coding style: Using StandaloneKindSignatures in GHC

[chessai]

The CLC owns base, with final say coming down to listed maintainers. Though
in practise, it ends up being a collective opinion of the CLC + GHC HQ that
drives decisions, rather than one person.

On Mon, May 24, 2021, 15:28 Oleg Grenrus <oleg.grenrus at iki.fi> wrote:

> To clarify, are you suggesting guidelines for GHC **and** base-library?
>
> I'm puzzled about ownership of base. Who have a final word about it?
> ghc-devs, libraries at haskell.org, CLC, chessai alone, whoever is first?
>
> - Oleg
> On 21.5.2021 23.21, Richard Eisenberg wrote:
>
> I agree with Chris here.
>
> Let me expand upon my counter-proposal:
>
> * A datatype declaration gets a standalone kind signature whenever at
> least one of its type arguments has a kind other than Type.
> * A class declaration gets a standalone kind signature whenever at least
> one of its type arguments has a kind other than Type.(*)
> * A closed type family always gets a standalone kind signature.
> * A type synonym gets a standalone kind signature whenever either at least
> one of its arguments has a kind other than Type or its result has a kind
> other than Type.
>
> (*) The class rule has an exception: if a class has a superclass
> constraint using Monad, Functor, Applicative, Foldable, or Traversable (or
> some other class whose name textually includes one of those names, such as
> MonadIO), we understand that the constrained variable must have kind Type
> -> Type. If that type variable is the only one without kind Type -> Type,
> then the standalone kind signature is optional.
>
> In cases other than those covered above, the standalone kind signature is
> optional, at the discretion of the programmer.
>
> This suggests that Dict gets a signature, Eq does not, Fix does, and
> Either does not.
>
> Richard
>
> On May 21, 2021, at 12:37 PM, Chris Smith <cdsmith at gmail.com> wrote:
>
> On Fri, May 21, 2021 at 2:11 AM Baldur Blöndal <baldurpet at gmail.com>
> wrote:
>
>> > encouraging the use of a standalone signature for type declarations
>> where at least one parameter of the datatype does not have kind Type.
>>
>> So Dict, Eq both get a sig but Fix and Either do not?
>>
>>   type Dict :: Constraint -> Type
>>   type Eq   :: Type -> Constraint
>>   type Fix  :: (Type -> Type) -> Type
>
>
>  That's not how I understand Richard's criteria.  Dict and Fix have
> non-Type parameters (Dict has a Constraint parameter, and Fix has a (Type
> -> Type) parameter.  On the other hand, Eq and Either have only Types as
> parameters.  This seems to match my intuition about when a kind signature
> might be helpful, as well as yours as far as I can tell from what you wrote.
>
> That's not to say I am advocating any kind of rule.  As I'm not really
> involved in GHC development, I refrain from having any opinion.  I just
> think you may have misread Richard's suggestion.
>
>
>
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