PostgreSQL BEFORE INSERT trigger with function

gistfile1.sql

# Function returns user.login, current year, the primary_key which is the id, in 5 length (Example: 00045) 
string format
# http://developer.postgresql.org/pgdocs/postgres/functions-formatting.html
# to_char(5,'00000') results the same number format
CREATE OR REPLACE FUNCTION "public"."function_name" () RETURNS trigger AS
'
BEGIN
    NEW.title = (SELECT login FROM users WHERE id = NEW.author) || to_char(NOW(),\'YYYY\') || lpad(NEW.id::char, 5, \'0\');
    RETURN NEW;
END
'
LANGUAGE 'plpgsql'

# Trigger 
CREATE TRIGGER "call_function"
BEFORE INSERT ON table_name FOR EACH ROW
EXECUTE PROCEDURE function_name()

# Show function invoked by trigger name in question in psql command line
select prosrc from pg_trigger,pg_proc where
 pg_proc.oid=pg_trigger.tgfoid
 and pg_trigger.tgname = '<name>'

# or (only show trigger thtat calls the function)
\d table_name