anchor.diff:    "Get the parent directory and update the minibuffer.
   
   Default keybindings: `M-Left' and `C-l'."
  -  (setf *current-directory* (uiop:pathname-parent-directory-pathname *current-directory*))
  +  (uiop:chdir "..")
     (erase-input minibuffer)
     (update-display minibuffer))
   
  
positive.code:   (let ((filename (get-candidate minibuffer)))
      (when (and (uiop:directory-pathname-p filename)
                 (uiop:directory-exists-p filename))
        (setf *current-directory* filename)
        (erase-input minibuffer)
        (update-display minibuffer))))
  
  
negative.code: ;;; - a UI to list files
  ;;; - lazy loading for large directories
  ;;; - many things...
  
  (defparameter *open-file-in-new-buffer* t
    "If non-t, don't open files and directories in a new buffer.")
  