(defun print-a ()
  (format *standard-output* "a")
  (finish-output)
  (sleep 1))

(defmacro read-thread(res)
  `(sb-thread:make-thread
    (lambda()(setf ,res (read *standard-input*)))))

(defun main ()
  (let* ((res nil)
	 (stop nil)
	 (thread (read-thread res)))
    (loop do
	 (if (null (sb-thread:thread-alive-p thread))
	     (case res
	       ((q)
		(return))
	       ((p)
		(and stop (print-a))
		(setf stop (not stop)
		      thread (read-thread res)))
	       (otherwise
		(unless stop (print-a))
		(setf thread (read-thread res))))
	     (unless stop (print-a))))))