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WCompatWarningsOn.hs:13:5: warning: [-Wmissing-monadfail-instances (in -Wcompat)]
• Could not deduce (Control.Monad.Fail.MonadFail m)
arising from the failable pattern ‘Just _’
(this will become an error in a future GHC release)
from the context: Monad m
bound by the type signature for:
monadFail :: Monad m => m a
at WCompatWarningsOn.hs:11:1-27
Possible fix:
add (Control.Monad.Fail.MonadFail m) to the context of
the type signature for:
monadFail :: Monad m => m a
• In a stmt of a 'do' block: Just _ <- undefined
In the expression:
do { Just _ <- undefined;
undefined }
In an equation for ‘monadFail’:
monadFail
= do { Just _ <- undefined;
undefined }
WCompatWarningsOn.hs:16:1: warning: [-Wsemigroup (in -Wcompat)]
Local definition of ‘<>’ clashes with a future Prelude name.
This will become an error in a future release.
WCompatWarningsOn.hs:22:3: warning: [-Wnoncanonical-monoid-instances (in -Wcompat)]
Noncanonical ‘(<>) = mappend’ definition detected
in the instance declaration for ‘Semi.Semigroup S’.
Move definition from ‘mappend’ to ‘(<>)’
WCompatWarningsOn.hs:25:3: warning: [-Wnoncanonical-monoid-instances (in -Wcompat)]
Noncanonical ‘mappend’ definition detected
in the instance declaration for ‘Monoid S’.
Define as ‘mappend = (<>)’
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