What about?:

instance Read e => MonadFail (Either e) where
    fail = Left . read

2018년 10월 25일 (목) 오후 12:42, David Feuer <david.feuer@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@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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