Reports & Discoverer :: Using Functions In Report Builder Program Unit

i am creating a report using a function in the select query..suppose this is my function that i created in the program unit of the report

FUNCTION is_numeric_rep (p_strval in varchar2) RETURN
NUMBER
IS
l_numval NUMBER;
BEGIN
l_numval := TO_NUMBER(p_strval);
RETURN 1;
EXCEPTION
WHEN OTHERS THEN
RETURN 0;
END is_numeric_rep;

and also suppose this is the query of the report

Select
is_numeric_rep('343aa43')
From dual

when pressing ok on the query statment in the report it give me this error: ORA-00904 "is_numeric_rep":invalid identifier although when i create this function as a stored function in the database schema and use it in the report it works fine with no problems.