Overloading

I never did get an answer to this.

I get:
ERROR: cannot change return type of existing function
HINT: Use DROP FUNCTION first.

********** Error **********

ERROR: cannot change return type of existing function
SQL state: 42P13
Hint: Use DROP FUNCTION first.

When I try to:

CREATE OR REPLACE FUNCTION check_date_ymd(given_date varchar)
RETURNS BOOLEAN AS
and
CREATE OR REPLACE FUNCTION check_date_ymd(given_date varchar, OUT
isvalid boolean, OUT ryear int, OUT rmonth int, OUT rday int) AS

I wanted to an 'is it valid' version, and another that would save
runtime by also returning values that would speed up the
function date_to_utime().

in pg_proc there is no 'check_date_ymd', so there is no 'collision'.

Can someone elucidate me on this?

Thanks!
Ralph