[ghc-steering-committee] Constraint vs Type: I propose acceptance

[Simon Peyton Jones]

| 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 <ghc-steering-committee-
| bounces at haskell.org> On Behalf Of Joachim Breitner
| Sent: 24 April 2018 03:45
| To: ghc-steering-committee at haskell.org
| Subject: Re: [ghc-steering-committee] Constraint vs Type: I propose
| acceptance
| 
| 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 at haskell.org
| > https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-
| committee
| --
| Joachim Breitner
|   mail at joachim-breitner.de
|   http://www.joachim-breitner.de/