anchor.diff:  (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."
  +  "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*)
  
positive.code:   (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.")
  
  (defun walk-form (form &optional (parent nil) (env (make-walkenv)))
    "Walk FORM and return a CLOS based AST that represents it."
  
negative.code:        :return (values data t)
       :finally
         (if error-p
             (error "No value for ~S of type ~S in environment ~S was found."
                    name type environment)
             (values default-value nil))))
  
  #+(or) ;; it's not used for now
  (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 (progn
               (setf (cddr env-piece) value)
               (return value))
       :finally
         (when error-p
           (error "No value for ~S of type ~S in environment ~S was found."
                  name type environment))))
  
  ;;;
  