Creating Functions & Triggers

Hello everyone, I'm new to creating functions & triggers on postgresql
and am having trouble creating a trigger to update a record with the
modification date and the current user.

My code is below, but doesn't work.  It hangs psql when I attempt to
modify the record.  The function and trigger are created successfully.

CREATE FUNCTION email_mod_date() RETURNS OPAQUE AS '
   BEGIN
         UPDATE email SET  m_date = current_date, m_by_user =
current_user
         WHERE id = NEW.id;

   RETURN NULL;
   END;
'LANGUAGE 'plpgsql';



CREATE TRIGGER email_mod_date
AFTER UPDATE
ON email
FOR EACH ROW
EXECUTE PROCEDURE email_mod_date();

Thanks for any help.

Kevin Lohka