anchor.diff:    (setf (buffer-ptr xp) 0)
     (setf (buffer-offset xp) (charpos xp))
     (setf (Qleft xp) 0)
  -  (setf (Qright xp) #.(- queue-entry-size))
  -  (setf (prefix-stack-ptr xp) #.(- prefix-stack-entry-size))
  +  (setf (Qright xp) (- +queue-entry-size+))
  +  (setf (prefix-stack-ptr xp) (- +prefix-stack-entry-size+))
     xp)
    
  
positive.code: 
  
  (eval-when (eval load compile)
  (defun structure-type-p (x)
    (and (symbolp x)
         (get x 'sys.int::structure-type)))
  
negative.code:   (setf (Qoffset xp (Qright xp)) nil)
    (setf (Qarg xp (Qright xp)) arg))
  
  (defmacro Qnext (index) `(+ ,index +queue-entry-size+))
  
  (defvar *describe-xp-streams-fully* nil "Set to T to see more info.")
  