Problem with some function

Hi!

i create some function like this

CREATE FUNCTION checkuser(varchar,varchar) RETURNS INTEGER AS '
DECLARE
user ALIAS FOR $1;
pwd ALIAS FOR $2;
BEGIN
SELECT id_user FROM users WHERE username=user AND password=pwd AND allow_login = ''true'';
IF id_user IS NULL THEN
RAISE NOTICE ''User not found'';
RETURN 0;
ELSE
UPDATE users SET last_login = ''NOW'', login_counts = login_counts+1;
RETURN id_user;
END IF;
END;
' LANGUAGE 'plpgsql';

What i want this function is to do? Check is username and pass is
correct and if it is, then update table users with last_login date and
counts this login.

WHen i execute this

devDbSir=# SELECT checkuser('uros','mypass');

i get this error.

ERROR: unexpected SELECT query in exec_stmt_execsql()

what am i doing wrong, please help me with this.

P.S. executin SELECT id_user...... myself it works. also update
sentence.
--
by,
Uros