anchor.diff:  (defparameter *clock* 0)
   
   (defparameter *out->in* (make-hash-table))
  -
  -(defparameter *in->act* (make-hash-table))
   
   
   
  
positive.code:   in)
  
  
  (defmethod i/o-connect ((in in-port) (act actor))
    (setf (gethash (id-of in) *in->act*)
  	act)
    act)
  
  
  (defmethod i/o-connected-p ((out out-port) (in in-port))
    (multiple-value-bind (value present-p)
        (gethash (id-of out) *out->in*)
      (and present-p
  	 (eq value in))))
  
  
  (defmethod i/o-connected-p ((in in-port) (act actor))
    (multiple-value-bind (value present-p)
        (gethash (id-of in) *in->act*)
      (and present-p
  	 (eq value act))))
  
  
  (defmethod components-list ((sim simulator))
  
negative.code:   (:documentation "Connect src to dest."))
  
  
  (defgeneric i/o-connected (src)
    (:documentation "Return values: connected object and connected-p
    boolean."))
  
  
  (defgeneric i/o-disconnect (src)
    (:documentation "Disconnect src."))
  
  
  
  