SQL & PL/SQL

I am wondering how to create a PL/SQL function with variable length argument lists. A good example of this is the LEAST function:

SELECT LEAST (1, 2, 3, 4, 5, 6, 7) FROM DUAL;
-- 1

I would like to create my own function which takes in any number of parameters as input. I've done some searching but cannot seem to find any documentation on this.

Thanks.