Using regoper type with OPERATOR()

Hello,

Say I have a discount table that stores either percentages or dollar
amounts, and I'd like to save the operator to be used in a
calculation. I started with a text field and CASE statement, but then
found the operator types that seem more useful:

CREATE TABLE discounts(price float, disc float, disc_oper regoperator);
INSERT INTO discounts VALUES
        (100, .1, '*(float, float)'),
        (100, 10, '-(float, float)');

so I could use a query like:

SELECT price OPERATOR(disc_oper::regoper) disc AS disc_amount FROM discounts

This doesn't work however, and I'm not sure why. I think I'm missing
something simple since:

SELECT disc_oper::regoper FROM discounts;
  disc_oper
--------------
 pg_catalog.*
 pg_catalog.-
(2 rows)

and

SELECT 100 OPERATOR(pg_catalog.*) .1;

make me think I'm very close.

Any help appreciated.

Thanks,

Tony