Using a VARCHAR2 in a SELECT command

Question

I'm trying to query for a given path in a hierarchy of products. However, I want to be able to have it return multiple values. So, I created a string in my function below that returns identifiers like "(34, 43, 54)" to be used in a SELECT IN. The function works fine, but the select command fails. How can I get the SELECT to work?
CREATE TABLE PRODUCT (
  PRODID NUMBER,
  PARENTID NUMBER,
  CATID NUMBER,
  ALIAS VARCHAR2(128)
CREATE OR REPLACE FUNCTION FIND_PRODS_BY_PATH
(CAT_ID IN NUMBER, IN_PATH IN VARCHAR2) RETURN VARCHAR2 IS
  PROD_IDS VARCHAR2(1024);
BEGIN
  PROD_IDS := '(';
  FOR PROD IN (SELECT PRODID, SYS_CONNECT_BY_PATH(ALIAS, '/') AS PATH FROM PRODUCT
    WHERE CATID=CAT_ID CONNECT BY PRIOR PRODID=PARENTID)
  LOOP
    IF REGEXP_LIKE(PROD.PATH, IN_PATH) THEN
      IF LENGTH(PROD_IDS) > 1 THEN
        PROD_IDS := PROD_IDS || ', ';
      END IF;
      PROD_IDS := PROD_IDS || PROD.PRODID;
    END IF;
  END LOOP;
  PROD_IDS := PROD_IDS || ')';
  RETURN PROD_IDS;
END FIND_PRODS_BY_PATH;
*** Doesn't like the varchar2 returned from the function ***
SELECT * FROM PRODUCT WHERE PRODID IN FIND_PROD_BY_PATH(5, '/my/product/path/*');
Error report:
SQL Error: ORA-01722: invalid number
*** Function works ***
SELECT FIND_PROD_BY_PATH(5, '/my/product/path/*') FROM DUAL;
FIND_PRODS_BY_PATH(5, '/my/product/path/*')                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         
(301152, 301202, 301252, 301302, 301403)

Answer 1

Your function is effectively returning a single string, which is not automatically devived into individual tokens for using in the IN clause.
How to circumvent this is best described here:
http://www.oracle.com/technology/oramag/oracle/07-mar/o27asktom.html
(search for "Varying IN Lists")