Re: Instance warnings [Re: Remove MonadFail (ST s) instance]

Some kind of instance warning like this would enable library authors to migrate type class instances. The Core Libraries Committee would likely be able to use this for good. I would definitely like to see that happen. Type class instances are "stuck" in Haskell today. On Tue, 26 Nov 2019 at 08:10, Oliver Charles wrote:

Perhaps I have found motivation for my first proposal!

On Mon, Nov 25, 2019 at 10:06 PM David Feuer wrote:

...

That definitely sounds like a good approach to me!

On Mon, Nov 25, 2019, 5:04 PM Oliver Charles wrote:

...

I wonder if like TypeError we could have TypeWarning? Then you could have something like

instance TypeWarning "Please use Fooble instead" => Show Foo where

which would compile, but produce a warning whenever the `Show Foo` constraint was solved?

On Mon, Nov 25, 2019 at 4:28 PM Andreas Abel wrote:

...

Derailing... Incidently, I recently asked for a "instance warning" feature in GHC:

https://gitlab.haskell.org/ghc/ghc/issues/17485

(In my case I could go with a TypeError constraint instead.)

Maybe instance warnings could be a useful feature. It could be implemented along the TypeError mechanism.

On 2019-11-24 18:35, Henning Thielemann wrote:

...

On Sun, 24 Nov 2019, Dan Burton wrote:

...

We're talking about an instance in `base`, so if there's no other way, it could at least be a flag akin to -Wmissing-monadfail-instances that gets included in -Wcompat. But relatedly: should there be a way to deprecate instances? I would say yes.

Sounds like another application of instance warnings that we already talked about: https://gitlab.haskell.org/ghc/ghc/issues/11796 _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries