anchor.diff:  (export '(timer
             timer-p
             timer-ms
  -          timer-repeat-p
  -          timer-last-time
  -          timer-function
             start-timer
             stop-timer
             alive-timer-p))
  
positive.code: (defun stop-timer (timer)
    (setq *timer-list* (delete timer *timer-list*)))
  
  (defun update-timer ()
    (let ((promised-timers)
          (update-p))
      (dolist (timer *timer-list*)
        (when (< (timer-ms timer)
                 (- (get-internal-real-time)
                    (timer-last-time timer)))
          (handler-case
  
negative.code: (defvar *timer-list* nil)
  
  (defstruct (timer (:constructor %make-timer))
    _ms
    repeat-p
    last-time
    function
  