Rule won't let me NOTIFY, no matter how hard I try

Here's the setup: I wanted to write a rule that would fire on an update
to one table, and do an update to another table, followed by a notify.
My first attempt wasn't acceptable to PG (7.3.4):

create rule "my_rule" as
on update to table_A
where new.col_A != old.col_A
do
(update table_B ...;
notify "my_signal";
);

... because you can't have a "notify" statement in a rule that fires on
update (only select, update, and delete, I guess).

Second attempt was to "hide" the notify in a function:

create function fn_notify(TEXT) returns VOID as '
execute ''notify " || $1 || "'';
' language 'plpgsql';

Oddly enough, this works IF and ONLY IF the rule "my_rule" fires and the
internal update statement does not update any rows. If it actually
updates a row, then I get this error:

WARNING: plpgsql: ERROR during compile of fn_notify near line 5
ERROR: syntax error at or near ""

What gives? Must I use a trigger to get around this?

--
Jeff Boes vox 269.226.9550 ext 24
Database Engineer fax 269.349.9076
Nexcerpt, Inc. http://www.nexcerpt.com
...Nexcerpt... Extend your Expertise