anchor.diff:                  #:less-first)
     (:export #:future
              #:ident
  -           #:done?
  +           #:done-p
              #:register-future
              #:complete-future
              #:make-future
  
positive.code: 
  (defun/cc wait-for (future)
    (let/cc continuation
      (if (not (done? future))
        (setf (completed-cb future) continuation)
        (funcall continuation)))
    (val future))
  
negative.code: (defparameter *actions* (seq))
  
  ;; functions
  (defun done-p (future)
    (slot-boundp future 'val))
  
  (defun make-future ()
  