; Characters
;  -  characters in scheme are just like the characters you on a keyboard
;      they contain letters, numbers, punctuation
;  - the interersting thing about them is how they are stored
;       - computers store data in binary, base 2, 0's and 1's
;         0's are stored as off or no voltage, 1's are stored as voltage
;      - characters are typcially stored with 8 bit (a bit is either 0 or 1)
;        we can make 2^8, or 256 different 8 bit binary numbers
;      - Scheme only uses 2^8 = 256, used 0 to 255 to represent characters,
;        but all the printable characters lie between 0 and 127

; Scheme has builtin procedures for converting between a character and
; its numerical representation
(char->integer #\a)   ;    #\  in front of a letter tells us we are talking about the character
(integer->char 97)

; make a list of the characters represented by the numbers from N to 0
(define list-of-chars
  (lambda (n)
    (if (< n 0)
        '()
        (cons (cons (integer->char n) n) (list-of-chars (- n 1))))))