anchor.diff:  ;;;
   ;;; A "written" boolean attribute is added to each varrec.
   
  -(define-walker classify-variables () ignore-domain)
  +(define-trivial-walker classify-variables ())
   
   (define (mark-variable varrec use)
     (varrec-attr-set! varrec 'state
  
positive.code:                     (quote (unquote nparams))
                      (arg-count ())))))))
  
  (define-walker reg-use (dest-type) ignore-domain)
  (define-walker codegen (dest in-frame-base out-frame-base regs out)
                 ignore-domain)
  
  ;;; Begin
  
  
negative.code: 
  (define (varrec-written? varrec) (varrec-attr varrec 'written))
  
  (define-trivial-walker eliminate-defines ())
  
  (define-eliminate-defines (define varrec . val)
    (rplaca form 'set!)
  