anchor.diff:    id
     lvl
     time
  +  tag
     msg)
   
   (defun read-log-message (stream)
  
positive.code: 					  :mapping (mapping-stream-mapping 
  						    (log-stream-stream log)))
  		   :header header
  		   :count (log-header-count header)
  		   :size (log-header-size header))))
  		 
  
negative.code: 		     (make-log-message :id (log-header-id (log-stream-header log))
  				       :lvl lvl
  				       :time (get-universal-time)
  				       :tag (log-stream-tag log)
  				       :msg (apply #'format nil format-control args)))
    (let ((index (advance-to-next-block log)))
      (incf (log-header-id (log-stream-header log)))
  