Lisp binary search

lisp2.2.clisp

(defun smaller()
	(setf *big* (1- (guess-my-number)))
		(guess-my-number))

(defun bigger()
	(setf *small* (1+ (guess-my-number)))
		(guess-my-number))

(defun guess-my-number()
	(ash (+ *small* *big*) -1))

(defun start-over ()
  (defparameter *small* 1)
  (defparameter *big* 100)
  (guess-my-number))