the use of expressions instead of simple values in array insertion?

Hi,
I encounter a problem whene I wanted use expressions to inset values in
column whose values are of array type.
the following example illustrates this problem:
CREATE TABLE address (Num INT4, street VARCHAR, city VARCHAR, contry
VARCHAR);
CREATE TABLE person (name VARCHAR, add OID[]);

CREATE FUNCTION address_oid (VARCHAR) returns OID AS'
SELECT OID from address s where s.city = $' LANGUAGE 'SQL';

INSERT INTO address VALUES (5, 'bd Les Champs Elizy', 'Paris' , 'France');
INSERT INTO address VALUES (10, 'Place Leclerc', 'Poitiers' , 'France');

the question is : how we can insert values in person table by using
address_oid function.
the solution I find is to make this in several steps :
INSERT INTO person VALUES ('Dupont', '{}');

Update person set add[1] = address_oid ('Poitiers');
Update person set add[1] = address_oid ('Paris');

can someone know how we can make this in one step without using update
commad.

thanks for your help,

Mourad.