;;; spell-number.el

(defun spell-999 (n)
  "Return English spelling of integer N (0<=N<=999)."
  (let 
      ((hundreds (/ n 100)) 
       (tens (/ (% n 100) 10))
       (units (% n 10)))
    (concat
     (if (> hundreds 0)
	 (concat (spell-unit hundreds) " hundred "))
     (cond 
      ((= tens 1) (spell-teens units))
      ((> tens 1)
       (concat
	(spell-tens tens)
	(if (> units 0) "-"))))
     (if (and (not (= tens 1)) (> units 0)) (spell-unit units)))))

(defun spell-unit (n)
  "Return spelling of single-digit integer N (1<=N<=9)."
  (cond
   ((= n 1) "one")
   ((= n 2) "two")
   ((= n 3) "three")
   ((= n 4) "four")
   ((= n 5) "five")
   ((= n 6) "six")
   ((= n 7) "seven")
   ((= n 8) "eight")
   ((= n 9) "nine")))

(defun spell-tens (n)
  "Return spelling of single-digit multiple of ten N (2<=N<=9)."
  (cond
   ((= n 2) "twenty")
   ((= n 3) "thirty")
   ((= n 4) "forty")
   ((= n 5) "fifty")
   ((= n 6) "sixty")
   ((= n 7) "seventy")
   ((= n 8) "eighty")
   ((= n 9) "ninety")))

(defun spell-teens (n)
  "Return spelling of 'teens' number corresponding to single-digit nteger N (0<=N<=9)."
  (cond
   ((= n 0) "ten")
   ((= n 1) "eleven")
   ((= n 2) "twelve")
   ((= n 3) "thirteen")
   ((= n 4) "fourteen")
   ((= n 5) "fifteen")
   ((= n 6) "sixteen")
   ((= n 7) "seventeen")
   ((= n 8) "eighteen")
   ((= n 9) "nineteen")))

(defun bottles-of-beer ()
  "Sing the song."
  (interactive)
  (progn
    (switch-to-buffer "*bottles-of-beer*")
    (dotimes (i 100)
      (let* 
	  ((n (- 100 i)) 
	   (number (spell-999 n))
	   (b (if (= n 1) "bottle" "bottles")))
	(insert
	 (if (< n 100) (format "%s %s of beer on the wall\n\n" number b) "")
	 (format "%s %s of beer on the wall\n%s %s of beer\nYou take one down, pass it around\n" number b number b))))
    (insert "no more bottles of beer on the wall\n")))