Re: [ghc-steering-committee] Treat kind and type vars identically with `forall` #103

Hi, Am Donnerstag, den 22.03.2018, 11:52 -0400 schrieb Richard Eisenberg:

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On Mar 22, 2018, at 11:15 AM, Simon Peyton Jones wrote:

Dear GHC steering committee I strongly propose that we accept Treat kind and type vars identically with `forall` #103

Agreed, unsurprisingly.

there seems to be consensus.

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Moreover, I propose that we adopt it without a 3-release wait after #83 – see under Alternatives. Any programs that are rejected by #103 can be fixed by adding some extra forall k’s. And that change will be accepted NOW if you add -XTypeInType.

Here I disagree. Enabling -XTypeInType has two unfortunate knock-on effects: - * is no longer available in kinds, without import Data.Kind. Happily, GHC gives a good error message upon a forgotten `import Data.Kind`, so this isn't so bad, but it will bite very widely. - More troublesomely, the CUSK rules are different with -XTypeInType than without. This means that turning on -XTypeInType can turn some CUSKs into non-CUSKs, producing utterly befuddling error messages. Maybe this won't bite so often, but when it does, it will take a developer a long time to sort out the problem.

After #83, these problems melt away, but I think it will be painful for users to support multiple versions in the meantime.

Richard

what does this mean for this proposal? Is there disagreement over quickly the proposal will be implemented? Cheers, Joachim -- Joachim Breitner mail@joachim-breitner.de http://www.joachim-breitner.de/