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

[Joachim Breitner]

Hi,

well, we were more liberal at deprecating things in the past than we
will be under the new regime, and we might not have invoked GR2 here.

But the extension already _is_ deprecated. If deprecating (even for the
wrong reasons) and waiting multiple releases does not allow us to break
the deprecated thing, then what is the point of GR3?

I am quite fond of the new stability regime, it sets out
clear requirements on code (set a language flag, heed deprecation
warnings, although the latter could be spelled out more explicitly), in
return for clear promises. Let’s not water this down by not taking the
set of requirements of requirements seriously ourselves.

Cheers,
Joachim

Am Montag, dem 29.01.2024 um 11:32 +0000 schrieb 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
> > 
> > 
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-- 
Joachim Breitner
  mail at joachim-breitner.de
  http://www.joachim-breitner.de/