1_number-list-starter.scm

;; PROBLEM:
;; Create function that satisfiy following example

(check-expect (number-list (list "first" "second" "third"))            
              (list "1: first" "2: second" "3: third"))
              
(define (number-list n) empty) ; stub

;; #1 Objective: 
;;     - Satisfy all design elements (or as much as posible)

2_number-list-solution.scm

;; (listof String) -> (listof String)
;; append each string's position in the list to the front of the string to number the list
(check-expect (number-list empty) empty)
(check-expect (number-list (list "first" "second" "third"))            
              (list "1: first" "2: second" "3: third"))
;(define (number-list los) los)   ;stub

#;
(define (number-list lon0)
  ;; acc: Natural; 1-based position of (first lon) in lon
  ;; (number-list (list "first" "second" "third") 1)
  ;; (number-list (list         "second" "third") 2)
  ;; (number-list (list                  "third") 3)
  (local [(define (number-list lon acc)
            (cond [(empty? lon) empty]
                  [else 
                   (... acc
                        (first lon)
                        (number-list (rest lon)
                                     (add1 acc)))]))]
    (number-list lon0 1)))



(define (number-list lon0)
  ;; acc: Natural; 1-based position of (first lon) in lon
  ;; (number-list (list "first" "second" "third") 1)
  ;; (number-list (list         "second" "third") 2)
  ;; (number-list (list                  "third") 3)
  (local [(define (number-list lon acc)
            (cond [(empty? lon) empty]
                  [else 
                   (cons (string-append (number->string acc) ": " (first lon))
                         (number-list (rest lon) (add1 acc)))]))]
    (number-list lon0 1)))