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