CREATE OR REPLACE PACKAGE mypkg
IS
    FUNCTION myfunc(p1 in varchar2,p2  number)
 return NUMBER;   

  cursor c1 is
   select 
      myfunc(a.col1, a.col2)  calculate_col
    from tabl a;
     
  
end my pkg;

SCOTT@orcl_12.1.0.2.0> CREATE TABLE tabl
  2    (col1  VARCHAR2(5),
  3  	col2  NUMBER)
  4  /

Table created.

SCOTT@orcl_12.1.0.2.0> INSERT INTO tabl VALUES ('3+2', 4)
  2  /

1 row created.

SCOTT@orcl_12.1.0.2.0> INSERT INTO tabl VALUES ('5-2', 4)
  2  /

1 row created.

SCOTT@orcl_12.1.0.2.0> CREATE OR REPLACE PACKAGE mypkg
  2  IS
  3    FUNCTION myfunc
  4  	 (p1 in varchar2,
  5  	  p2	number)
  6  	 return NUMBER;
  7    cursor c1 is
  8  	 select mypkg.myfunc(a.col1, a.col2) calculate_col
  9  	 from	tabl a;
 10    PROCEDURE test_proc;
 11  end mypkg;
 12  /

Package created.

SCOTT@orcl_12.1.0.2.0> SHOW ERRORS
No errors.
SCOTT@orcl_12.1.0.2.0> CREATE OR REPLACE PACKAGE BODY mypkg
  2  IS
  3    FUNCTION myfunc
  4  	 (p1 in varchar2,
  5  	  p2	number)
  6  	 return NUMBER
  7    IS
  8  	 v_result NUMBER;
  9    BEGIN
 10  	 EXECUTE IMMEDIATE
 11  	   'SELECT (' || p1 || ')*' || p2 || ' FROM DUAL'
 12  	   INTO v_result;
 13  	 RETURN v_result;
 14    END myfunc;
 15    PROCEDURE test_proc
 16    IS
 17    BEGIN
 18  	 FOR r1 IN c1 LOOP
 19  	   DBMS_OUTPUT.PUT_LINE (r1.calculate_col);
 20  	 END LOOP;
 21    END test_proc;
 22  END mypkg;
 23  /

Package body created.

SCOTT@orcl_12.1.0.2.0> SHOW ERRORS
No errors.
SCOTT@orcl_12.1.0.2.0> EXEC mypkg.test_proc
20
12

PL/SQL procedure successfully completed.