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
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
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