Remove MonadFail (ST s) instance

[David Feuer]

How do you deprecate an instance?

On Sun, Nov 24, 2019, 12:18 PM Dan Burton <danburton.email at gmail.com> wrote:

> If someone depends on this behavior, we should give them the courtesy of a
> proper deprecation cycle to aid them in fixing their code. That's what a
> deprecation cycle is for. Don't skip it.
>
> -- Dan Burton
>
>
> On Sun, Nov 24, 2019 at 7:57 AM Oleg Grenrus <oleg.grenrus at iki.fi> wrote:
>
>> I cannot see any justification for that instance
>>
>>      -- | @since 4.11.0.0
>>      instance Fail.MonadFail (ST s) where
>>          fail s = errorWithoutStackTrace s
>>
>> If someone wants to fail pattern matches in `ST s`, please do that
>> explicitly.
>>
>> I suggest and propose the removal without any deprecation period. If
>> someone depends on this behavior, they ought to fix they code
>> immediately: it's straight forward compiler type-error driven refactoring.
>>
>> Note: compatibility package
>>
>> https://hackage.haskell.org/package/fail-4.9.0.0/docs/Control-Monad-Fail.html
>> doesn't have that instance, so I suspect not-that many use(d) that
>> instance.
>>
>> Discussion period: 2 weeks (until Monday 2019-12-09).
>>
>> - Oleg
>>
>> P.S. you might run into problems  with
>> https://gitlab.haskell.org/ghc/ghc/issues/15681 bug/miss-feature, but
>> there's always a workaround to write code using explicit matching
>> combinator, so it's not a show stopper.
>>
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