Re: [Haskell-cafe] Deprecation cycle for classes

On Sat, Jun 15, 2019 at 11:51:33PM -0400, Viktor Dukhovni wrote:

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On Jun 15, 2019, at 12:20 PM, Tom Ellis 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