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

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/princi...

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 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/princi... 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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