MonadFailErrors.hs:16:5: error:
    • 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 :: Monad m => m a
        at MonadFailErrors.hs:14:1-25
      Possible fix:
        add (MonadFail m) to the context of
          the type signature for:
            general :: 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:30:5: error:
    • 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:44:5: error:
    • No instance for (MonadFail (ST s))
        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 ‘st’:
          st
            = do { Just x <- undefined;
                   undefined }

MonadFailErrors.hs:51:5: error:
    • 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 }