#!/usr/local/bin/sbcl --script
(in-package #:cl-user)
(defpackage #:beer
  (:use #:common-lisp)
  (:export #:verse #:sing))
(in-package #:beer)

;; [*endpoint-min*, *endpoint-max*] in notations for intervals.
(defparameter *endpoint-max* 99)
(defparameter *endpoint-min* 0)

(defun generate-1st-line (n)
  (format nil
          "~a bottle~p of beer on the wall, ~a bottle~p of beer."
          (if (= 0 n) "No more" n)
          n
          (if (= 0 n) "no more" n)
          n))

(defun generate-2nd-line (n)
  (if (= *endpoint-min* n)
    (format nil
            "Go to the store and buy some more, ~a bottle~p of beer on the wall."
            *endpoint-max*
            *endpoint-max*)
    (let ((n-1 (1- n)))
      (format nil
              "Take ~a down and pass it around, ~a bottle~p of beer on the wall."
              (if (= *endpoint-min* n-1) "it" "one")
              (if (= *endpoint-min* n-1) "no more" n-1)
              n-1))))

(defun verse (n)
  (format nil
    "~a~&~a~&"
    (generate-1st-line n)
    (generate-2nd-line n)))

(defun sing (&optional (start *endpoint-max*) (end *endpoint-min*))
  (format nil
          "~{~a~%~}"
          (loop for i from start downto end
                collect (verse i))))

(format t (sing))