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

[Simon Marlow]

"Only exceptionally would we fix a design flaw in a way that breaks
programs compiled with existing language editions."
https://github.com/ghc-proposals/ghc-proposals/blob/wip/general-rules/principles.rst#34exceptions-gr2

This is not exceptional is it? It's just a regular design flaw :) If we
must fix it, let's do it in a way that complies with the stability
principle.

Cheers
Simon


On Mon, 29 Jan 2024 at 11:15, Joachim Breitner <mail at joachim-breitner.de>
wrote:

> Hi,
>
> Am Montag, dem 29.01.2024 um 11:03 +0000 schrieb Simon Marlow:
> > I might be a bit confused, but doesn't this proposal change the meaning
> of an existing
> > extension (PatternSignatures)?
>
> a long-ago deprecated one:
>
> ~ $ ghci
> GHCi, version 9.4.8: https://www.haskell.org/ghc/  :? for help
> ghci> :set -XPatternSignatures
>
> <no location info>: warning: [-Wdeprecated-flags]
>     -XPatternSignatures is deprecated: use -XScopedTypeVariables or pragma
> {-# LANGUAGE ScopedTypeVariables #-} instead
>
> Hopefully our stability principles does not require us to heed programs
> that ignored deprecation flags for a while?
>
> My understanding of
>
> https://github.com/ghc-proposals/ghc-proposals/blob/wip/general-rules/principles.rst#3ghc-stability-principles
> is that, despite “stable package” not saying “does not use features
> deprecated long ago”, it’s still ok to break such programs, as this is
> our mechanism GR3?
>
>
> Of course we could side-step this procedural question about repurposing
> an old extension and introduce `SimplePatternSignatures` instead. Not
> in favor, simply because as a user I more than once intuitively reached
> for `PatternSignatures` to get the proposed behavior.
>
> Cheers,
> Joachim
>
>
> --
> Joachim Breitner
>   mail at joachim-breitner.de
>   http://www.joachim-breitner.de/
>
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