anchor.diff:  ;;; is expanded.
   
   (define-compiler-macro go (label)
  -  (aif (assoc label *tagbody-replacements*)
  +  (aif (cdr (assoc label *tagbody-replacements*))
       `(vm-go ,!)
       (with-gensym g
         (acons! label g *tagbody-replacements*)
  
positive.code:      ,@(mapcar #'((x)
   	                (if (consp x)
  		     		    x
  		     			(aif (assoc x *tagbody-replacements*)
  		       				!
  		       				x)))
                 args)
  
negative.code:   `(vm-scope ,@(vars-to-identity body)))
  
  (defun lookup-create-gensym (block-name)
    (or (cdr (assoc block-name *blockname-replacements*))
        (with-gensym g
          (acons! block-name g *blockname-replacements*)
          g)))
  