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MonadFailWarnings.hs:19:5: warning: [-Wmissing-monadfail-instances (in -Wcompat)]
• Could not deduce (MonadFail m)
arising from the failable pattern ‘Just x’
(this will become an error in a future GHC release)
from the context: Monad m
bound by the type signature for:
general :: forall (m :: * -> *) a. Monad m => m a
at MonadFailWarnings.hs:17:1-25
Possible fix:
add (MonadFail m) to the context of
the type signature for:
general :: forall (m :: * -> *) a. Monad m => m a
• In a stmt of a 'do' block: Just x <- undefined
In the expression:
do Just x <- undefined
undefined
In an equation for ‘general’:
general
= do Just x <- undefined
undefined
MonadFailWarnings.hs:35:5: warning: [-Wmissing-monadfail-instances (in -Wcompat)]
• No instance for (MonadFail Identity)
arising from the failable pattern ‘Just x’
(this will become an error in a future GHC release)
• In a stmt of a 'do' block: Just x <- undefined
In the expression:
do Just x <- undefined
undefined
In an equation for ‘identity’:
identity
= do Just x <- undefined
undefined
MonadFailWarnings.hs:51:5: warning: [-Wmissing-monadfail-instances (in -Wcompat)]
• No instance for (MonadFail (ST s))
arising from the failable pattern ‘Just x’
(this will become an error in a future GHC release)
• In a stmt of a 'do' block: Just x <- undefined
In the expression:
do Just x <- undefined
undefined
In an equation for ‘st’:
st
= do Just x <- undefined
undefined
MonadFailWarnings.hs:59:5: warning: [-Wmissing-monadfail-instances (in -Wcompat)]
• No instance for (MonadFail ((->) r))
arising from the failable pattern ‘Just x’
(this will become an error in a future GHC release)
• In a stmt of a 'do' block: Just x <- undefined
In the expression:
do Just x <- undefined
undefined
In an equation for ‘reader’:
reader
= do Just x <- undefined
undefined
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