#! /usr/bin/clisp

;;; per default zeigen die Karten tux
(defstruct card
  (front 'tux)
  (back  'tux) )

(defconstant allcards 
  (vector (make-card)
          (make-card :front 'gates :back 'gates)
          (make-card :back 'gates) ))

(defun flipcard (c)
  (make-card :front (card-back c) :back (card-front c)) )

(defun maybeflipcard (c)
  (if (zerop (random 2))
      c
      (flipcard c) ))

(defun randomcard ()
  (maybeflipcard (svref allcards (random 3))) )

;;; kein Lisp-Programm ohne Makro
(defmacro whentux (v &rest body)
  `(when (eq ,v 'tux) ,@body) )

;;; alles bereit, jetzt wird gezaehlt
(do ((card (randomcard) (randomcard))
     (fronttux 0)
     (bothtux  0) )
    ((= fronttux 1000) (format t "~,2,2f %" (/ bothtux fronttux)))
  (whentux (card-front card)
    (incf fronttux)
    (whentux (card-back card)
      (incf bothtux) )))