Postgres Create Function syntax error

Recently updated databases from 8.4 to 9.0. Instead of doing full dump and restore, I am moving items over and cleaning up along the way.

We have a function called generate_recurrences (originally: http://justatheory.com/computers/databases/postgresql/recurring_events.html).

I have create the datatype recurrence, but when I try to create the function, I get the error:
ERROR:  syntax error at or near "check"
LINE 37:             WHILE to_char(next_date, 'DD') <> check LOOP

CREATE DOMAIN recurrence AS TEXT
CHECK ( VALUE IN ( 'none', 'daily', 'weekly', 'monthly' ) );

CREATE OR REPLACE FUNCTION  generate_recurrences(
    recurs RECURRENCE, 
    start_date DATE,
    end_date DATE
)
    RETURNS setof DATE
    LANGUAGE plpgsql IMMUTABLE
    AS $BODY$
DECLARE
    next_date DATE := start_date;
    duration  INTERVAL;
    day       INTERVAL;
    check     TEXT;
BEGIN
    IF recurs = 'none' THEN
        -- Only one date ever.
        RETURN next next_date;
    ELSIF recurs = 'weekly' THEN
        duration := '7 days'::interval;
        WHILE next_date <= end_date LOOP
            RETURN NEXT next_date;
            next_date := next_date + duration;
        END LOOP;
    ELSIF recurs = 'daily' THEN
        duration := '1 day'::interval;
        WHILE next_date <= end_date LOOP
            RETURN NEXT next_date;
            next_date := next_date + duration;
        END LOOP;
    ELSIF recurs = 'monthly' THEN
        duration := '27 days'::interval;
        day      := '1 day'::interval;
        check    := to_char(start_date, 'DD');
        WHILE next_date <= end_date LOOP
            RETURN NEXT next_date;
            next_date := next_date + duration;
            WHILE to_char(next_date, 'DD') <> check LOOP
                next_date := next_date + day;
            END LOOP;
        END LOOP;
    ELSE
        -- Someone needs to update this function, methinks.
        RAISE EXCEPTION 'Recurrence % not supported by generate_recurrences()', recurs;
    END IF;
END;
$BODY$;

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