anchor.diff:    "A measurement that is only emitted when leaving a monitoring region.
   Its value is the corresponding monitoring region start.")
   
  -(defun call-with-monitoring-region (name thunk)
  -  (let* ((*measurements* *measurements*)
  -         (start (make-monitoring-region-start name)))
  -    (store-measurement start *measurements*)
  -    (unwind-protect
  -         (let ((*context* (cons name *context*)))
  -           (funcall thunk))
  -      (let ((end (make-monitoring-region-end name start)))
  -        (setf (measurement-value start) end)
  -        (store-measurement end *measurements*)))))
  -
   (defmacro with-monitoring-region ((name) &body body)
     "Execute BODY in a region monitoring NAME.  This entails the following things:
   
  
positive.code:         (store-measurement measurement storage))))
    (values))
  
  (defgeneric store-measurement (measurement storage))
  
  (defmethod print-object ((measurement measurement) stream)
    (if *print-pretty*
  
negative.code:    measurement."
    `(call-with-monitoring-region ',name (lambda () ,@body)))
  
  (defun call-with-monitoring-region (name thunk)
    (let* ((*measurements* *measurements*)
           (start (make-monitoring-region-start name)))
      (store-measurement start *measurements*)
      (unwind-protect
           (let ((*context* (cons name *context*)))
             (funcall thunk))
        (let ((end (make-monitoring-region-end name start)))
          (setf (measurement-value start) end)
          (store-measurement end *measurements*)))))
  
  (defmethod print-object ((monitoring-region-start monitoring-region-start) stream)
    (print-unreadable-object (monitoring-region-start stream :type t)
      (format stream "~@{~S ~S~^ ~}"
  