anchor.diff:  
   (defclass keyword-function-argument-form (function-argument-form)
     ((keyword-name :accessor keyword-name-of :initarg :keyword-name)
  -   (default-value :accessor default-value-of :initarg :default-value)
  +   (default-value :initform nil :accessor default-value-of :initarg :default-value)
      (supplied-p-parameter :accessor supplied-p-parameter :initarg :supplied-p-parameter)))
   
   (defun effective-keyword-name-of (k)
  
positive.code:       (intern (symbol-name (name-of k)) :keyword)))
  
  (defun walk-keyword-argument (form parent env)
    (destructuring-bind (name &optional default-value supplied-p-parameter)
        (ensure-list form)
      (let ((name (if (consp name)
                      (second name)
  
negative.code:       `(,name ,specializer)))
  
  (defclass optional-function-argument-form (function-argument-form)
    ((default-value :initform nil :accessor default-value-of :initarg :default-value)
     (supplied-p-parameter :accessor supplied-p-parameter :initarg :supplied-p-parameter)))
  
  (defun walk-optional-argument (form parent env)
    (destructuring-bind (name &optional (default-value nil default-value-supplied?) supplied-p-parameter)
        (ensure-list form)
      (with-form-object (arg 'optional-function-argument-form parent
                             :name name
                             :supplied-p-parameter supplied-p-parameter)
        (when default-value-supplied?
          (setf (default-value-of arg) (walk-form default-value arg env))))))
  
  (defunwalker-handler optional-function-argument-form (name supplied-p-parameter)
    (let ((default-value (unwalk-form (default-value-of -form-))))
  