;; A 3mechs is
;;   (make-3mechs <symbol> <symbol> <symbol>)
;;
(define-struct 3mechs (recent two-ago three-ago))

; Example of data:
;
(make-3mechs 'Mike 'Patty 'Bubba)


; Template:
;

#|
(define (process-3mech a-3m)
  ..(3mechs-recent a-3m)..(3mechs-two-ago a-3m)..(3mechs-three-ago a-3m)..)
|#

;; update-mechs: 3mechs, symbol --&gt; 3mechs
#|
(define (update-mechs a-3m newest-mech)
  ..(3mechs-recent a-3m)..(3mechs-two-ago a-3m)..(3mechs-three-ago a-3m)..)
|#
#|
; Tests
(process-3mech (make-3mechs 'Mike 'Patty 'Bubba) 'Mike)
  = (make-3mechs 'Mike 'Mike 'Bubba)


; ian: sentinels

; Better soln:

;; A symbol-or-false is
;;    - a symbol, or
;;    - false
;;
;; A 3mechs is:
;;    (make-3mechs <symbol-or-false> <symbol-or-false> <symbol-or-false>)

 |#




 #|
;; A structure for a cons ("constructed list"):
(define-struct cons (first rest))

;Examples of data:
(make-cons 'Bubba empty)


; Data definition for List-of-Symbols:

;; A List-of-Symbols is either
;;	- empty, or
;;	- (make-cons <symbol> <List-of-Symbols>)

;; Examples of data:

empty

(make-cons 'Bubba empty)

(make-cons 'Mike 
           (make-cons 'Patty 
	                     (make-cons 'Bubba
		                                empty)))

; How would you get Mike out of this list?


; How would extract Patty out of this list?


;; Trick question:
;(cons-first empty)
;(cons-rest empty)

  |#


;; times-served : list-of-symbols -> number
;; Determine the length of the list of mechanics' names.
;;
(define (times-served mechs) ...)

; Examples:
;