How to run a select these parameters in the function? to figure out the date that is being used

CREATE OR REPLACE FUNCTION fact(text DEFAULT to_char((('now'::text)::date - '00:00:00'::interval), ('YYYYMM'::text || '01'::text)), text DEFAULT to_char((((to_char((('now'::text)::date)::timestam p with time zone, 'YYYY'::text) || '1231'::text))::date)::timestamp with time zone, 'yyyymmdd'::text))
RETURNS void AS