T7148a.hs:19:50:
    Could not coerce from ‘Result a b’ to ‘b’
      because ‘Result a b’ and ‘b’ are different types.
      arising from the coercion of the method ‘coerce’ from type
                   ‘forall b. Proxy b -> a -> Result a b’ to type
                   ‘forall b. Proxy b -> IS_NO_LONGER a -> Result (IS_NO_LONGER a) b’
    Possible fix:
      use a standalone 'deriving instance' declaration,
        so you can specify the instance context yourself
    When deriving the instance for (Convert (IS_NO_LONGER a))