;; largest:  list-of-number (non-empty) -> number
;; consumes a non-empty list of numbers and produces the largest number in the list
(define (largest alon)
  (largest-accum (rest alon) (first alon)))

;; largest-accum:  list-of-number number -> number
;; consumes a list of numbers and produces the largest number in the list,
;; keeping track of the largest number seen so far in largest-so-far
(define (largest-accum alon largest-so-far)
  (cond [(empty? alon) largest-so-far]
        [(cons? alon) 
         (cond [(> (first alon) largest-so-far)
                (largest-accum (rest alon) (first alon))]
               [else (largest-accum (rest alon) largest-so-far)])]))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;;   Change Language Level to Advanced
;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;


;; an account is a struct
;; (make-account number number)
(define-struct account (acctnum balance))

;; a list-of-account is etiehr
;; empty, or 
;; (cons account list-of-account)

;; Citibank:  list-of-account
;; remembers the current contents of each bank account
(define Citibank (list (make-account 1 500)
                       (make-account 2 1000)
                       (make-account 3 10)))

;; original version of add-account, doesn't change Citibank
; ;; add-account:  number number list-of-account -> list-of-account
;;;; makes a new account with the given account number and balance, and
;;;; adds the account to the list 
; (define (add-account acctnum amt aloa)
;   (cons (make-account acctnum amt) aloa))
; 


;; add-account:  number number  -> void
;; makes a new account with the given account number and balance, and
;; adds the account to the list
;; EFFECT:  adds an account to Citibank
(define (add-account acctnum amt)
  (set! Citibank (cons (make-account acctnum amt) Citibank)))


;; ticketnum: number
;; stores the last ticket number handed out
(define ticketnum 0)

;; get-ticket:  -> number
;; produces the next ticket number
;; EFFECT:  increments ticketnum, or restarts it at 1
(define (get-ticket)
  (begin
    (cond [(= 4 ticketnum) (set! ticketnum 1)]
          [else (set! ticketnum (+ 1 ticketnum))])
    ticketnum))