Coding style: Using StandaloneKindSignatures in GHC

[Carter Schonwald]

Yeah that’s roughly exactly it

On Mon, May 24, 2021 at 4:37 PM chessai <chessai1996 at gmail.com> wrote:

> 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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