MonadFailErrors.hs:14:5: error: [GHC-39999]
    • Could not deduce ‘MonadFail m’
        arising from a do statement
        with the failable pattern ‘Just x’
      from the context: Monad m
        bound by the type signature for:
                   general :: forall (m :: * -> *) a. Monad m => m a
        at MonadFailErrors.hs:12:1-25
      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

MonadFailErrors.hs:28:5: error: [GHC-39999]
    • No instance for ‘MonadFail Identity’
        arising from a do statement
        with the failable pattern ‘Just x’
    • 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

MonadFailErrors.hs:42:5: error: [GHC-39999]
    • No instance for ‘MonadFail ((->) r)’
        arising from a do statement
        with the failable pattern ‘Just x’
    • 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