so f g
    where
        f (x :- t) = Just (URI x Nothing :- t)
        g (URI x _ :- t) = Just (x :- t)

instance
isoURI = Iso f g
    where
        f (x :- t) = Just (URI x Nothing :- t)
        g (URI x _ :- t) = Just (x :- t)
isoURI = Iso f g
    where
        f (x :- t) = Just (URI x Nothing :- t)
        g (URI x _ :- t) = Just (x :- t)