5010-examples/06-4-lasns.rkt at master · mwand/5010-examples · GitHub

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;; A ListOfAlternatingNumbersAndStrings (LANS) is one of:
;; -- empty
;; -- (cons Number LASN)

;; A ListOfAlternatingStringsAndNumbers (LASN) is one of:
;; -- empty
;; -- (cons String LANS)

;; lans-fn : LANS -> ??
;; (define (lans-fn lans)
;;   (cond
;;     [(empty? lans) ...]
;;     [else (...
;;             (first lans)
;;             (lasn-fn (rest lans)))]))

;; lasn-fn : LASN -> ??
;; (define (lasn-fn lasn)
;;   (cond
;;     [(empty? lasn) ...]
;;     [else (...
;;             (first lasn)
;;             (lans-fn (rest lasn)))]))

;; strategy: Use template for LANS/LASN on lans
;; lans-sum : LANS -> Number
(define (lans-sum lans)
  (cond
    [(empty? lans) 0]
    [else (+
            (first lans)
            (lasn-sum (rest lans)))]))

;; lasn-sum : LASN -> Number
(define (lasn-sum lasn)
  (cond
    [(empty? lasn) 0]
    [else (lans-sum (rest lasn))]))