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:               (error "Sorry, no walker for the special operator ~S defined." (car form)))
               (t (gethash 'application *walker-handlers*))))))
  
  (defmacro defwalker-handler (name (form parent lexenv)
                               &body body)
    `(progn
       (setf (gethash ',name *walker-handlers*)
             (lambda (,form ,parent ,lexenv)
               (declare (ignorable ,parent ,lexenv))
               ,@body))
       ',name))
  
  