SQL & PL/SQL

Hi,

I have a Function who returns in priview:

(1,2,3,4)

Now i am using this function in SQL where clause

Select from debug where id in debug.debug_process()

On execute select i am getiing ORA-01722 invalid number , i understand that functions return not only numbers but  character symbols too '(,)'

Are it posible to use user defined function who do not return NUMBER in Where clause IN statement ?  If not what tips can sugest me for getting list of values for use in IN Clause?

ID.

Thanks!