anchor.diff:    (lambda (env)
       (let ((uid (get-uid env)))
         `(200 (:content-type "text/html")
  -            ,(append (page-header)
  +            ,(append (page-header env)
                        (if uid                       
                            (list "<p>You are already logged in as " uid ".</p>")
                            (login-form))
  
positive.code:           (let* ((session (getf env :lack.session))
                   (url (gethash :prev-url session "/")))
              (setf (gethash :uid session "/") name)
              `(303 (:location ,url) ("")))
            (redirect-to-login-page)))))
  
  
negative.code:            ;; /privateにmountしているのでpathには/privateが含まれない
             (path (concatenate 'string "/private" (getf env :path-info))))
        `(200 (:content-type "text/html")
              ,(append (page-header env)
                       (status uid)
                       (list "<p>Private Area: path = " path "</p>")
                       (page-footer))))))
  