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@despammed.com