India's Horizon phone company, founded in 2010, stores phone numbers in their local area switches according to the following structure and data definitions:

  (define-struct phone (area switch num))
  ;; A PhoneNumber is a structure: 
  ;;   (make-phone AC SC SWON)

  ;; An AC is a natural number between 200 and 999

  ;; A SC is a natural number between 200 and 999

  (define-struct swon (d1 d2 d3 d4))
  ;; A SWON is a structure: 
  ;;   (make-swon Digit Digit Digit Digit)

  ;; A Digit is one of: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9

Their programs deal with recording the phone calls, directing them, monitoring hardware failures, etc. To increase their profit, however, they have off-shored the creation of phone bills to your CheapHacks company, located in cheap-labor Bos-tone. Your boss has asked you to do the following over the weekend:

1. Translate the CCIS office phone number, which is (617) 373-2461, into Horizon's data representation.

   
   

   
   

   Solution:

   Grader: Theo

     ;; [PTS: 1]
     (make-phone 617 373 (make-swon 2 4 6 1))
   

2. Design the function report, which consumes a phone number and produces a string, according to standard convention. For example, the representation of the CCIS office phone number would produce "(617) 373-2461". Hint: number->string converts a number (digit) into a string; string-append juxtaposes strings.

   
   

   
   

   Solution:

     ;; report : PhoneNumber -> String [PTS 1]
     ;; convert the given phone number into a string [PTS 1]
     (define (report pn) 
       ;; [PTS 2: 1 for the selectors, 1 for correctness]
       (string-append 
        "(" (number->string (phone-area pn)) ")"
        " "
        (number->string (phone-switch pn))
        "-"
        (swon-report (phone-num pn))))
   
     ;; [PTS +3 if correctly in-lined]
     ;; swon-report : SWON -> String [PTS 1]
     ;; convert the given swon to a string [PTS 1]
     (define (swon-report s)
       ;; [PTS 2: selectors, correctness]
       (string-append (number->string (swon-d1 s))
                      (number->string (swon-d2 s))
                      (number->string (swon-d3 s))
                      (number->string (swon-d4 s))))
   
     ;; TESTS: [PTS 2, 1 per function]
     (equal? (swon-report (make-swon 2 4 6 1))
             "2461")
     (equal? (report 
               (make-phone 617 373 (make-swon 2 4 6 1)))
             "(617) 373-2461")
   

3. If Horizon decides to change the structure definition for phone to

     (define-struct phone (area switch local))
   

   at how many places and how do you have to change your solution?

   
   

   
   

   Solution:

     [PTS 1 for full answer]
     once, I must replace phone-num with phone-local 
     XOR [if they in-lined]
     four, I must replace all phone-num/s with phone-local/s