cycling through custom type fields

Hello,

I would like to ask if there is a possibility in postgresql (v9) to
cycle through the fields of some custom type parameter in plpgsql function.

I have a type defined:
CREATE TYPE naims.frt_pwd_ed AS
    (pwd_id integer,
     pwd_sub_id integer,
     pwd_login character varying(100));

In pseudocode thats what I'd like to achieve:

function Changes(prm_old_pwd  naims.frt_pwd_ed, prm_new_pwd
naims.frt_pwd_ed)
returns set of text
begin
   FOR i = 0 to naims.frt_pwd_ed.FieldCount -1 LOOP
     IF prm_old_pwd.field(i).value <> prm_new_pwd.field(i).value THEN
       Return Next prm_old_pwd.field(i).fieldname;
     END IF;
   END LOOP;
   Return;
end;

The functrion should check each field of 2 provided parameters and
return the fieldnames where the values are different. For this I need
some tools to extract field value and field name. Can this be done?

Thank You in advance!

--
Julius Tuskenis
Programavimo skyriaus vadovas
UAB nSoft
mob. +37068233050