anchor.diff:    (unwalk-form (walk-form form nil (make-walkenv env))))
   
   (defvar *warn-undefined* nil
  -  "When non-NIL any references to undefined functions or variables will signal a warning.")
  +  "When non-NIL, any references to undefined functions or variables will signal a warning.")
   
   (defun walk-form (form &optional (parent nil) (env (make-walkenv)))
     "Walk FORM and return a CLOS based AST that represents it."
  
positive.code:        :return (values data t)
       :finally
         (if error-p
             (error "Sorry, No value for ~S of type ~S in environment ~S found."
                    name type environment)
             (values default-value nil))))
  
  #+(or)
  (defun (setf %lookup) (value environment type name &key (error-p nil))
    (loop
       for env-piece in environment
       when (and (eql (first env-piece)  type)
                 (eql (second env-piece) name))
         do (setf (cddr env-piece) value) and
         return value
       finally
         (when error-p
           (error "Sorry, No value for ~S of type ~S in environment ~S found."
                  name type environment))))
  
  ;;;
  
negative.code: (defparameter +atom-marker+ '+atom-marker+)
  
  (defun find-walker-handler (form)
    "Simple function which tells us what handler should deal with FORM. Signals an error if we don't have a handler for FORM."
    (if (atom form)
        (gethash '+atom-marker+ *walker-handlers*)
        (aif (gethash (car form) *walker-handlers*)
  