Using rowtype as function argument

Hi all,

I suppose this must be easy to figure out, but I can't find it anywhere in
the documentation.

How do I call a function that takes a rowtype for an argument as in:

CREATE FUNCTION myfunc(mytablename) RETURNS INT AS '
BEGIN
-- Do stuff
RETURN val;
END;
' LANGUAGE 'plpgsql'

How do I call this function? I haven't been able to figure it out or find
it anywhere...

Thanks in advance,

Martin