anchor.diff:  
   (defclass throw-form (form)
     ((tag :accessor tag :initarg :tag)
  -   (value :accessor value :initarg :value)))
  +   (value :accessor value-of :initarg :value)))
   
   (defwalker-handler catch (form parent env)
     (destructuring-bind (tag &body body)
  
positive.code:           (ecase type
              (setq (with-form-object (setq setq-form :parent parent :source form
                                            :variable-name var)
                      (setf (value setq) (walk-form value setq env))))
              (setf (walk-form (first effective-code) parent env))))
          ;; multiple forms
          (with-form-object (progn progn-form :parent parent :source form)
  
negative.code:     :accessor variable-name-of
      :initarg :variable-name)
     (value
      :accessor value-of
      :initarg :value)))
  
  (defwalker-handler setq (form parent env)
  