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@xyzzy.dhs.org <mailto:drew@xyzzy.dhs.org> 
http://xyzzy.dhs.org/~drew/ <http://xyzzy.dhs.org/%7Edrew/>
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