Beer song in Lisp

beer-song.lisp

(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)

A more elegant way of expressing plurals can be to make use of format's builtin ~p directive. See this as an example:
https://gist.github.com/fchurca/d788c9df76d4491fb625