<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">I agree with Chris here.<div class=""><br class=""></div><div class="">Let me expand upon my counter-proposal:</div><div class=""><br class=""></div><div class="">* A datatype declaration gets a standalone kind signature whenever at least one of its type arguments has a kind other than Type.</div><div class="">* A class declaration gets a standalone kind signature whenever at least one of its type arguments has a kind other than Type.(*)</div><div class="">* A closed type family always gets a standalone kind signature.</div><div class="">* 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.</div><div class=""><br class=""></div><div class="">(*) 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.</div><div class=""><br class=""></div><div class="">In cases other than those covered above, the standalone kind signature is optional, at the discretion of the programmer.</div><div class=""><br class=""></div><div class="">This suggests that Dict gets a signature, Eq does not, Fix does, and Either does not.</div><div class=""><br class=""></div><div class="">Richard</div><div class=""><br class=""></div><div class=""><div><blockquote type="cite" class=""><div class="">On May 21, 2021, at 12:37 PM, Chris Smith <<a href="mailto:cdsmith@gmail.com" class="">cdsmith@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div dir="ltr" class="">On Fri, May 21, 2021 at 2:11 AM Baldur Blöndal <<a href="mailto:baldurpet@gmail.com" target="_blank" class="">baldurpet@gmail.com</a>> wrote:<br class=""></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">> encouraging the use of a standalone signature for type declarations where at least one parameter of the datatype does not have kind Type.<br class="">
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So Dict, Eq both get a sig but Fix and Either do not?<br class="">
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type Dict :: Constraint -> Type<br class="">
type Eq :: Type -> Constraint<br class="">
type Fix :: (Type -> Type) -> Type</blockquote><div class=""><br class=""></div><div class=""> 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.</div><div class=""><br class=""></div><div class="">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.</div></div></div>
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