As suggested in the GHC Trac [1], it would be nice to have a MonadFail
instance for Either. The original suggestion by lexi.lambda was
instance MonadFail (Either String) where
fail = Left
However, it was rightfully pointed out that this instance is overly
specific. The discussion arrived at the following alternative proposed
by Iceland_jack:
instance IsString str => MonadFail (Either str) where
fail = Left . fromString
For previous discussion on this proposal, please take a look at the Trac
thread.
I am looking forward to your input!
Tobias
[1] GHC Trac Ticket #12160, https://ghc.haskell.org/trac/ghc/ticket/12160
--
Tobias Markus
"They who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."
-- Benjamin Franklin (1706-1790)
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