anchor.diff:  (defun make-arg-ast (index)
     (make-instance 'arg-ast :index index))
   
  +(defmethod stream-draw-ast ((ast arg-ast) stream)
  +  (format stream "   ~a [style = filled, fillcolor = orange];~%" (id ast))
  +  (format stream "   ~a [label = \"~a\"];~%"
  +	  (id ast)
  +	  (index ast)))
  +
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
   ;;; Class HALT-AST.
  
positive.code: (defun make-argcount-ast ()
    (make-instance 'argcount-ast))
  
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; Class ARG-AST.
  
negative.code:   (stream-draw-ast (body-ast ast) stream)
    (format stream "   ~a -> ~a~%"
  	  (id ast)
  	  (id (body-ast ast)))
    (stream-draw-ast (argparse-ast ast) stream)
    (format stream "   ~a -> ~a~%"
  	  (id ast)
  	  (id (argparse-ast ast))))
    
  (defmethod children ((ast function-ast))
    (list (body-ast ast)))
  