Constraint vs Type: I propose acceptance

Friends I propose that we support the GHC proposal "Declare Constraint is not apart from Typehttps://github.com/ghc-proposals/ghc-proposals/blob/rae/constraint-vs-type/p..." Currently GHC operates an uneasy compromise: * Constraint and Type are treated as distinct in the type checker (e.g. do not unify) * But they are treated as the same in Core I have spent ages in discussion with Richard and others for how to fix this wart. Really, they should be either * completely different (like Int and Bool), or * completely the same (like [Char] and String). But both these stances have problems, and nothing satisfying has emerged. So this proposal simply fixes the worst aspect (unsoundness) of the current setup. So I regard it as a way to stay explicitly non-committal, leaving the main question open. There are a couple of clarifications I'd like which I've put on the discussion thread. Simon

Hi, nobody responds to this in two months. I assume that we all simply trust Simon here? Simon, did you get the clarifications that you wanted? Can we go ahead and accept this? Cheers, Joachim Am Montag, den 26.02.2018, 11:14 +0000 schrieb Simon Peyton Jones:
Friends I propose that we support the GHC proposal “Declare Constraint is not apart from Type” Currently GHC operates an uneasy compromise: Constraint and Type are treated as distinct in the type checker (e.g. do not unify) But they are treated as the same in Core I have spent ages in discussion with Richard and others for how to fix this wart. Really, they should be either completely different (like Int and Bool), or completely the same (like [Char] and String). But both these stances have problems, and nothing satisfying has emerged. So this proposal simply fixes the worst aspect (unsoundness) of the current setup. So I regard it as a way to stay explicitly non-committal, leaving the main question open. There are a couple of clarifications I’d like which I’ve put on the discussion thread. Simon _______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee -- Joachim Breitner mail@joachim-breitner.de http://www.joachim-breitner.de/

Yes, that sounds right to me. Manuel
Am 24.04.2018 um 12:45 schrieb Joachim Breitner
: Hi,
nobody responds to this in two months. I assume that we all simply trust Simon here?
Simon, did you get the clarifications that you wanted? Can we go ahead and accept this?
Cheers, Joachim
Am Montag, den 26.02.2018, 11:14 +0000 schrieb Simon Peyton Jones:
Friends I propose that we support the GHC proposal “Declare Constraint is not apart from Type” Currently GHC operates an uneasy compromise: Constraint and Type are treated as distinct in the type checker (e.g. do not unify) But they are treated as the same in Core I have spent ages in discussion with Richard and others for how to fix this wart. Really, they should be either completely different (like Int and Bool), or completely the same (like [Char] and String). But both these stances have problems, and nothing satisfying has emerged. So this proposal simply fixes the worst aspect (unsoundness) of the current setup. So I regard it as a way to stay explicitly non-committal, leaving the main question open. There are a couple of clarifications I’d like which I’ve put on the discussion thread. Simon _______________________________________________ ghc-steering-committee mailing list ghc-steering-committee@haskell.org https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee -- 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

| Simon, did you get the clarifications that you wanted? Can we go ahead
| and accept this?
Yes -- let's just accept and move on.
It's a small proposal that rejects a few programs that are currently accepted, but should not be. After discussion Richard moved a much more elaborate proposal to a historical appendix; it wasn't "obviously right" enough to pay its way. But we may hope that in the future we will see more clearly, and so this proposal is deliberately a minimal holding position.
But the present situation is outright wrong, so there's a net step forward.
Simon
| -----Original Message-----
| From: ghc-steering-committee

Hi, Am Dienstag, den 24.04.2018, 20:48 +0000 schrieb Simon Peyton Jones:
Yes -- let's just accept and move on.
done! Cheers, Joachim -- Joachim Breitner mail@joachim-breitner.de http://www.joachim-breitner.de/
participants (3)
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Joachim Breitner
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Manuel M T Chakravarty
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Simon Peyton Jones