[SQL] how to create this trigger?

[Ramiro Arenas Ramírez]

I need to create a trigger that increment a value in a column 
of table1 where a row is inserted in table 2

I have tried whit this but it just does nothing.

CREATE FUNCTION increment_value () RETURNS opaque AS 
'DECLARE
   code int4;
   BEGIN
   code := new.code;
   UPDATE table1 
   SET value = value + 1
   WHERE id = code;
RETURN NEW;
END;'  LANGUAGE 'plpgsql';

CREATE TRIGGER insert_on_table2 BEFORE INSERT ON table2 
        FOR EACH ROW EXECUTE PROCEDURE increment_value();


Can you help me?