MonadFail instance for Either

[David Feuer]

No, that's awful. You'd need to write things like

    fail "\"my mistake\""

On Wed, Oct 24, 2018, 11:51 PM Dannyu NDos <ndospark320 at gmail.com> wrote:

> What about?:
>
> instance Read e => MonadFail (Either e) where
>     fail = Left . read
>
> 2018년 10월 25일 (목) 오후 12:42, David Feuer <david.feuer at gmail.com>님이 작성:
>
>> FWIW, I think I'm weakly opposed. Either is Haskell 98. MonadFail is
>> solidly "standards-track" material, to the extent that designation is
>> meaningful
>> at the moment. IsString ... isn't.
>> On Wed, Oct 24, 2018 at 10:44 PM Daniel Bergey <bergey at alum.mit.edu>
>> wrote:
>> >
>> > Is there still consensus in favor of adding this instance?
>> >
>> >  instance IsString str => MonadFail (Either str) where
>> >     fail = Left . fromString
>> >
>> > In 2016 there was some discussion, and my reading is that there was
>> consensus in favor at the time:
>> > Trac: https://ghc.haskell.org/trac/ghc/ticket/12160
>> > libaries mailing list:
>> https://mail.haskell.org/pipermail/libraries/2016-August/027248.html
>> >
>> > Does anyone know of a later decision not to add it, or was it simply no
>> one's top priority?
>> >
>> > What is the next step to move this proposal forward?  Is more
>> discussion in order?  Should I just submit a patch?
>> >
>> > Thanks,
>> > bergey
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>
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