;; Simple number guessing game in Common Lisp

(defmacro while (condition &body body)
  "While `condition' is not nil, evaluate `body'."
  `(loop while ,condition do (progn ,@body)))

(defun make-random (max)
  "Generate a random number up to `max' using a new random state."
  (let ((*random-state* (make-random-state t)))
    (random max)))

(defun read-integer ()
  (parse-integer (read-line *query-io*) :junk-allowed t))

(defun attempt-guess (number)
  "Run one round of a number guessing game where `number'
is the number the user is trying to guess."
  (let ((guess nil)
        (incorrect t))
    (loop do
      (format *query-io* "Enter a number: ")
      (force-output *query-io*)
      (setf guess (read-integer))
      (format t
              (cond
                ((< guess number) "The number is larger than ~D~%")
                ((> guess number) "The number is smaller than ~D~%")
                (t "Correct! The number was ~D~%"))
              guess)
      (when (= guess number)
        (setf incorrect nil))
      while incorrect))
  t)

(defun begin-number-guessing-game (&key one-shot (maximum 100))
  "If `one-shot' is t, run one round of a number guessing game.
Otherwise run a chain of games until the user wants to stop.

In both cases, `:maximum' is the maximum possible number."
  (when one-shot
    (return-from begin-number-guessing-game
      (attempt-guess (make-random maximum))))

  (let ((playing nil))
    (loop do
          (attempt-guess (make-random maximum))
          (setf playing (y-or-n-p "Play again?"))
          (format t "~%")
          while playing)))