readMaybe :: Read a => String -> Maybe a
readMaybe s = case readEither s of
                Left _  -> Nothing
                Right a -> Just a

readFail :: (MonadFail f, Read a) => String -> f a
readFail s = case readEither s of
                Left e  -> fail e
                Right a -> return a

readAlt :: (Alternative f, Read a) => String -> f a
readAlt s = case readEither s of
                Left _  -> empty
                Right a -> pure a