A function which returns all rolname from pg_roles.

How do I make this function work?  I am trying to get all the rolnames
from pg_roles.

CREATE OR REPLACE FUNCTION test() SETOF name AS $$
DECLARE
rrol  name;
BEGIN
SELECT rolname INTO rrol FROM pg_roles;
RETURN setof rrol;
END;
$$ LANGUAGE plpgsql;


regards,