simple recursive function in plpgsql fails

ians=# SELECT version();
version
---------------------------------------------------------------
PostgreSQL 7.1.3 on i686-pc-linux-gnu, compiled by GCC 2.95.4

My goal is to find the last occurance of a pattern in a string. As a
helper function, I wrote this:

DROP FUNCTION reverse(text);
CREATE FUNCTION reverse(text) RETURNS text AS
'DECLARE str ALIAS FOR $1;
BEGIN IF length(str) > 1 THEN
RETURN reverse(substr(str, 2)) || substr(str, 1, 1);
ELSE
RETURN str;
END IF;
END;' LANGUAGE 'plpgsql'

ians=# SELECT reverse('q');
reverse
---------
q
(1 row)

ians=# SELECT reverse('qw');
reverse
---------
wq
(1 row)

ians=# SELECT reverse('qwe');
reverse
---------
ewq
(1 row)

ians=# SELECT reverse('qwer');
reverse
---------
rerq
(1 row)

Ooops...

------------------------------------------------------------------------
Andrew G. Hammond drew(at)xyzzy(dot)dhs(dot)org <mailto:drew(at)xyzzy(dot)dhs(dot)org>
http://xyzzy.dhs.org/~drew/ <http://xyzzy.dhs.org/%7Edrew/>
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