triggers and functions in pgsql 7.0.2

I'm going through your docs trying to create a function and a trigger that
calls said function, what I've gotten so far is

CREATE FUNCTION create_count_cache()
RETURNS opaque AS
'
BEGIN;
DELETE FROM SnipCount;
INSERT INTO SnipCount SELECT LangID, COUNT(LangID) AS CNT FROM
snippet GROUP BY LangID;
COMMIT;
'
LANGUAGE 'sql';

CREATE TRIGGER count_change
AFTER DELETE OR INSERT ON snippet FOR EACH ROW
EXECUTE PROCEDURE create_count_cache();

however LANGUAGE sql cannot return opaque and plpgsql is not a known lang
type.

it seems that all your docs are a bit out of date, can you give me some help
please?

marc britten