(defun plural (n)
  (if (> n 1) "s" ""))

(defun beer-song (n)
  (format t "~a bottle~a of beer on the wall.~%" n (plural n))
  (format t "~a bottle~a of beer.~%" n (plural n))
  (format t "Take one down.~%")
  (format t "Pass it around.~%")

  (decf n)

  (if (> n 0)
    (progn
      (format t "~a bottle~a of beer on the wall.~%" n (plural n))
      (beer-song n))
    (format t "No more bottles of beer on the wall.~%")))

(beer-song 99)