anchor.diff:  ;;;
   ;;; This datum corresponds to a reference to a global FUNCTION,
   ;;; i.e., a function defined in the global environment.  
  -;;;
  -;;; In later compilation stages, this datum is eliminated.  Instead
  -;;; an EXTERNAL-INPUT is used to hold the storage cell containing the
  -;;; global value, i.e. the function object that is referred to.
   
   (defclass global-input (datum)
  -  ((%name :initarg :name :reader name)
  -   (%storage :initarg :storage :reader storage)))
  -
  -(defun make-global-input (name storage)
  +  ((%name :initarg :name :reader name)))
  +
  +(defun make-global-input (name)
     (make-instance 'global-input
  -    :name name
  -    :storage storage))
  +    :name name))
   
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  
positive.code: ;;;
  ;;; Instruction ENTER-INSTRUCTION.
  ;;;
  ;;; This instruction is mostly a placeholder for backend to put
  ;;; information that needs to be present right at the beginning of
  ;;; each procedure.  It has a single successor.
  
  (defclass enter-instruction (instruction)
    ())
  
  (defun make-enter-instruction (&optional (successor nil successor-p))
    (make-instance 'enter-instruction
      :successors (if successor-p (list successor) '())))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  
negative.code: ;;; Datum class SPECIAL-LOCATION.
  ;;;
  ;;; This datum corresponds to a reference to a special variable.
  
  (defclass special-location (datum)
    ((%name :initarg :name :reader name)))
  