;; long-words:  ListOfString -> ListOfString
;; produces a list of words with more than 5 characters
(define (long-words alos0)
  (local [(define (long-words alos acc)
            (cond [(empty? alos) acc]
                  [(cons? alos) (if (> (string-length (first alos)) 5)
                                    (long-words (rest alos) (cons (first alos) acc))
                                    (long-words (rest alos) acc))]))]
    (long-words alos0 empty)))

(define-struct account (acctnum balance))
;; an Account is a (make-account Natural Number)
;; where acctnum is the account number
;; balance is the balance in the account (in dollars)

;; a ListOfAccount is one of
;; empty
;; (cons Account ListOfAccount)


;; Citibank:  ListOfAccount
;; remembers the information about each account in the list
(define Citibank (list (make-account 1 500)
                       (make-account 2 1000)
                       (make-account 3 10)))

;; add-account:  Natural Number -> void
;; makes a new account and adds it to Citibank
;; EFFECT: changes the contents of Citibank
(define (add-account acctnum amt)
  (set! Citibank
        (cons (make-account acctnum amt) Citibank)))