Create trigger for auto update function

Hi to all,

I have a table:
create table hoy(
id serial,
pass varchar(40),
pass_md5 varchar(40);

Now, I want to write a trigger function that automatically updates the pass_md5 with the md5 function of the pass.

I tried this:

CREATE FUNCTION update_pass(integer) RETURNS integer AS $$
UPDATE hoy SET pass_md5=md5(pass) WHERE id=$1;
SELECT 1;
$$ LANGUAGE SQL;

and

CREATE TRIGGER triger_users_pass_md5
AFTER INSERT OR UPDATE
ON hoy
EXECUTE PROCEDURE update_pass(integer);

But it works not.
When I create the trigger it says that function does not exist.

I also tried with:

CREATE OR REPLACE FUNCTION user2(integer)RETURNS TRIGGER AS'
BEGIN
UPDATE users SET pass_md5=md5(pass) WHERE id=$1;
return NULL;
END
'language plpgsql;
.... the same

Need some help!!!!

Andy.