[Haskell-cafe] Deprecation cycle for classes

[Viktor Dukhovni]

On Sun, Jun 16, 2019 at 08:02:20AM +0100, Tom Ellis wrote:

> On Sat, Jun 15, 2019 at 11:51:33PM -0400, Viktor Dukhovni wrote:
> > > On Jun 15, 2019, at 12:20 PM, Tom Ellis <tom-lists-haskell-cafe-2017 at jaguarpaw.co.uk> wrote:
> > > 
> > > I am unsure how to change the name of a class in a library whilst providing
> > > a safe deprecation cycle for the users of the library.  Suppose I have
> > > version 1 of my library with a class
> > 
> > Is this perhaps essentially:
> > 
> >    https://gitlab.haskell.org/ghc/ghc/issues/7543
> 
> It's closely related and indeed option 2 that Edward Yang proposes below
> would allow me to do what I want:
> 
>     "Allow instance declarations on constraint synonyms, but only if after
>     desugaring the synonym, you end up with a single class head."
> 
>     https://gitlab.haskell.org/ghc/ghc/issues/13267

Your motivation sounds quite reasonable, though the issues appear
to be difficult, maybe if you ask again there'll be a different
answer this time?

-- 
	Viktor.