maybeRead :: Read a => String -> Maybe a
maybeRead s = case reads s of
                  [(x,"")]    -> Just x
                  _           -> Nothing
maybeRead :: Read a => String -> Maybe a
maybeRead s = case reads s of
                  [(x,"")]    -> Just x
                  _           -> Nothing
maybeRead s = case reads s of
                  [(x,"")]    -> Just x
                  _           -> Nothing