[ghc-steering-committee] Proposal #608, -XPatternSignatureBinds. Rec: accept

Richard Eisenberg rae at richarde.dev
Mon Feb 26 13:29:50 UTC 2024

> On Jan 29, 2024, at 6:03 AM, Simon Marlow <marlowsd at gmail.com> wrote:
> I might be a bit confused, but doesn't this proposal change the meaning of an existing extension (PatternSignatures)? In which case shouldn't we do it properly according to our stability principles and either introduce the new behaviour as a new extension, or restrict the change to GHC2024 and later only?

Picking up this thread again (sorry for the delay).

As a reminder to all, about where we stand: This is about a small change to the deprecated extension -XPatternSignatures (which has been deprecated for at least as long as I've been doing Haskell). I personally don't see much merit in the change (it seems to achieve its goal only in a world where -XScopedTypeVariables is somehow deprecated, and that world seems unlikely to me), but neither do I see much downside. John Ericson, the proposer, sees an upside to the change, as does Joachim. We had basically settled leaning toward acceptance. Simon M wonders above about how this interacts with our stability principles.

In response to Simon: I think this is fine w.r.t. our stability principles, which include (GR3), saying that any change should come with a deprecation period. -XPatternSignatures has been deprecated for over a decade, which I think is sufficiently long. On the other hand, the deprecation doesn't describe the upcoming change, but I still think it's OK.


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