plpgsql recursion

Greetings!
I have a table like:

node parent
1 2
2 3
3 4

Since i traverse this table with a recursive function, i want to avoid
infinite recursion loop. I have wrote a function to check that a new record
does not create a circular dependency. The function i wrote is as follow:

CREATE OR REPLACE FUNCTION dba_test(INTEGER,INTEGER) RETURNS TEXT AS '
DECLARE
traversing ALIAS FOR $1;
testing ALIAS FOR $2;
t_rec RECORD;
BEGIN
FOR t_rec IN SELECT node,parent FROM dba_test WHERE parent = traversing
LOOP
IF t_rec.node = testing THEN
RETURN ''Circular'';
ELSE
PERFORM dba_test(t_rec.node,testing);
END IF;
END LOOP;
RETURN ''ok'' || testing::text;
END;
' LANGUAGE 'plpgsql';

I would use this function BEFORE inserting the new row. But if i try SELECT
dba_test(4,1); i don't have the result i expect. Can i you give me an hint
where am i wrong?

Thank you!

Stefano Vita Finzi
kluge(at)despammed(dot)com