Integer Value is Not a Number in Common Lisp?

When I execute the following Common Lisp program by calling `(play)`, I get the error: `Argument X is not a NUMBER: Guess` ``` ;;;; number-game.lisp ;;;; ;;;; Andrew Levenson ;;;; 10/25/2010 ;;;; ;;;; Simple number guessing game. User has ;;;; five guesses to determine a number between ;;;; one and one hundred, inclusive (1-100). ;;; Set global variable for the target number: (defparameter *target* nil) ;;; Set the iterator so we may check the number of guesses (defparameter *number-of-guesses* 0) ;;; Welcome the user (defun welcome-user () (format t "Welcome to the number guessing game!~%")) ;;; Prompt for a guess (defun prompt-for-guess () (format t "Please enter your guess (1-100): ") (finish-output nil) ; nil directs finish-output to standard IO (check-guess 'read-guess)) ;;; Read in a guess (defun read-guess () (let ((guess (parse-integer(read-line *query-io*)))) (if (numberp guess) ; If true, return guess. Else, call prompt-for-guess (progn (setq *number-of-guesses* (+ *number-of-guesses* 1)) 'guess) (prompt-for-guess)))) ;;; Check if the guess is higher than, lower than, or equal to, the target (defun check-guess (fn) (let ((guess (funcall fn))) (if (= guess *target*) (equal-to) (if (> guess *target*) (greater-than (guess)) (if (< guess *target*) (less-than (guess))))))) ;;; If the guess is equal to the target, the game is over (defun equal-to () (format t "Congratulations! You have guessed the target number, ~a!~%" *target*) (y-or-n-p "Play again? [y/n] ")) ;;; If the guess is greater than the target, inform the player. (defun greater-than (guess) (format t "Sorry, ~a is greater than the target.~%" guess) (if (< *number-of-guesses* 6) (prompt-for-guess) (game-over))) ;;; If the guess is less than the target, inform the player. (defun less-than (guess) (format t "Sorry, ~a is less than the target.~%" guess) (if (< *number-of-guesses* 6) (prompt-for-guess) (game-over))) ;;; If the player has run out of guesses, give them the option ;;; of playing the game again. (defun game-over () (y-or-n-p "You have run out of guesses. Play again? [y/n] ")) ;;; Play the game (defun play () ;; If it's their first time playing this session, ;; make sure to greet the user. (unless (> *number-of-guesses* 0) (welcome-user)) ;; Reset their remaining guesses (setq *number-of-guesses* 0) ;; Set the target value (setq *target* ;; Random can return float values, ;; so we must round the result to get ;; an integer value. (round ;; Add one to the result, because ;; (random 100) yields a number between ;; 0 and 99, whereas we want a number ;; from 1 to 100 inclusive. (+ (random 100) 1))) (if (equal (prompt-for-guess) "y") (play) (quit))) ``` What am I doing wrong that `guess` is not a number value in `check-guess`?