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: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