(defun make-guess (lower-bound upper-bound)
  (let ((guess (+ (random (- upper-bound lower-bound)) lower-bound))
	(response nil))
    ;; (format t "Lower bound: ~d; upper bound ~d~%" lower-bound upper-bound)
    (format t "How about ~d? Too high (2)? Too low (1)? Or am I right (0)?~%" guess)
    (setq response (read-line))
    (cond ((string-equal response "2")
	   (too-high guess lower-bound upper-bound))
	  ((string-equal response "1")
	   (too-low guess lower-bound upper-bound))
	  ((string-equal response "0")
	   (format t "I am so smart!~%"))
	  (t (format t "Eh?")
	     (make-guess lower-bound upper-bound)))))

(defun too-high (guess lower-bound upper-bound)
  (cond ((= guess lower-bound)
	 (format t "Cheater!~%")
	 (make-guess lower-bound (1+ upper-bound)))
	(t (make-guess lower-bound (1- guess)))))

(defun too-low (guess lower-bound upper-bound)
  (cond ((= guess (1- upper-bound))
	 (format t "Cheater!~%")
	 (make-guess (1- lower-bound) upper-bound))
	(t (make-guess (1+ guess) upper-bound))))

(defun play-guessing-game ()
  (let ((lower-bound 0) (upper-bound 1000))
    (format t "Think of a number between ~d and ~d~%" lower-bound upper-bound)
    (make-guess lower-bound upper-bound)))