;; A teachpack with some string <--> number helper functions,
;; for Comp280 04.spring hw09.
;;
;; Your program will use the "Add teachpack..." menu item of drscheme,
;; to gain access to these functions.
;; If you copy this file to your own machine,
;; note that the file name must match the module name ("hw09lib", in this case).
;; For further info on writing your own teachpacks, see:
;;    http://www.owlnet.rice.edu/~comp210/02fall/Handouts/teachpack-demo.shtml
;;
(module hw09lib  (lib "plt-pretty-big-text.ss" "lang")
  (provide 
     ; Convert bewteen a string and a list of ascii character codes:
     string->integers   ;:string -> (list-of int)
     integers->string   ;:(list-of int) -> string
     )
     ; Note that the next four functions are already built-in:
     ;
     ; Convert between a character and its ascii character code: 
     ;  char->integer  ;:char -> int
     ;  integer->char  ;:int -> char
     ; Convert between a string and a list of characters:
     ;  list->string   ;:(list-of char) -> string
     ;  string->list   ;:string -> (list-of char)


  ;; string->integers   :string -> (list-of int)
  ;; integers->string   :(list-of int) -> string
  ;; Convert bewteen a string an a list of ascii character codes.
  ;;
  (define (string->integers str)  (map char->integer (string->list str)))
  (define (integers->string nums) (list->string (map integer->char nums)))

  )

;; Test cases
; (string->integers "ABBA") = (list 65 66 66 65)
; (integers->string (list 66 65 66 65)) = "BABA"




;;    Scheme notes
;;
;; In scheme, the character 'w' is represented as #\w.
;; (E.g., (make-string 5 #\o) = "ooooo").
;; Some special characters include #\space, #\tab, and #\newline.
;;
;; The difference between the built-in functions "remainder" and "modulo"
;; is how they handle negative numbers:
;;    (remainder -7 5) = -2
;;    (modulo    -7 5) =  3.
;;
;;
;; Some scheme functions you shouldn't need to use, but are related:
;;   char-whitespace? 
;;   char-upper-case?   char-lower-case?   char-locale-upper-case? ..
;;   char-upcase        char-downcase      char-locale-upcase      ..
;; As always, see helpdesk for further info.