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