Functions returning RECORD

I have a question about syntax and feasibility.

I do the following:

CREATE FUNCTION xyz(int, int) RETURNS RECORD AS '...'
CREATE TABLE abc(a int, b int);

Now I want to call my xyz function once for each row in abc and I want
my RECORD to be (x int, y int, z timestamptz). How do I write that
query? I.e. where do specify my RECORD definition? Is it possible at
all? Ideally I'd like to write something like this:

SELECT xyz(a, b) AS (x int, y int, z timestamptz) FROM abc;

but that yields a syntax error.

Regards,
Thomas Hallgren