Re: [ghc-steering-committee] Discussion on proposal #99: forall {k}

OK -- I could agree with forbidding braces on `data` (given that the GADT-syntax alternative exists), but what about `class`? And then if we allow it on `class`, it seems a bit silly not to do the analogous thing on `data`. (Note that the proposal currently describes the same scheme as I have described in this email thread, but only about `class`.) Richard

On May 2, 2018, at 9:48 AM, Joachim Breitner wrote:

Hi,

Am Dienstag, den 01.05.2018, 22:05 -0400 schrieb Richard Eisenberg:

...

We can boil it down to one rule for these situations: RULE. Braces used in type declarations affect only the types of terms declared within the declaration. The braces have no effect whatsoever on the kind of the type(s) declared.

With this in mind, I'll answer the questions below:

...

On May 1, 2018, at 12:56 PM, Iavor Diatchki wrote:

-- 1) The "normal" case. I've written the types of the introduces names underneath, are they correct? data T1 {k} (a :: k) = C1 -- T1 :: forall {k::Type}. k -> Type -- C1 :: forall {k::Type} (a :: k). T1 {k} a

I would say we get

T1 :: forall (k :: Type) -> k -> Type -- T1 has *2* visible arguments C1 :: forall {k :: Type} (a :: k). T1 k a -- C1 has one inferred and one specified type argument

I think this is highly confusing. The {k} is on T1, but it does not affect T1, but rather something else?

What is wrong with “if you want to have different specificity on the tycon and the datacon, use GADTSyntax”?

Cheers, Joachim -- Joachim Breitner mail@joachim-breitner.de http://www.joachim-breitner.de/ _______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee