anchor.diff:  	 (if (null ,bind-vars)
   	     result
   	     `((lambda
  -		,(nreverse ,bind-vars) ,result) . ,(nreverse ,bind-vals))))))))
  +		,(nreverse ,bind-vars) ,result) . ,(nreverse ,bind-vals)))))))
   
   (defmacro with-variables (symbols &body body)
     "Using gensyms is necessary to prevent variables produced by macro expansions
  
positive.code:          (values form))
         ,@body)))
  
  (eval-when (:compile-toplevel :load-toplevel :execute)
  (defmacro once-only (variable-list &body body)
    "Generate code that evaluates certain expressions only once.
  This is used in macros, for computing expansions.
  
negative.code:          (handler-bind ,binds
             (:retry))))))
  
  (defmacro with-gensyms (syms &body body)
    `(let ,(mapcar #'(lambda (s)
                       `(,s (gensym)))
                   syms)
       ,@body))
  
  
  (defvar *file-if-exists* :supersede
  