swap-window-buffers.el

(defun swap-window-buffers ()
  (interactive)
  (let (siblings
        (child (window-child (window-parent)))
        (src-win (selected-window))
        (src-buf (window-buffer))
        dest-win
        dest-buf)
    (message
     (catch 'except
       (if (or (eq (frame-root-window) src-win)
               (not (window-parent)))
           (throw 'except "Cannot swap!"))
       (while child
         (when (window-live-p child)
           (setq siblings (cons child siblings)))
         (setq child (window-next-sibling child)))
       (if (and (> (length siblings) 1)
                (eq (car siblings) src-win))
           (setq dest-win (car (last siblings)))
         (setq dest-win
               (catch 'dest
                 (cl-mapl #'(lambda (tail)
                              (if (eq (car tail) src-win)
                                  (throw 'dest (cadr tail))))
                          (reverse siblings))
                 nil)))
       (if (not dest-win)
           (throw 'except "Cannot swap!"))
       (setq dest-buf (window-buffer dest-win))
       (condition-case nil
           (mapc #'(lambda (pair)
                     (set-window-buffer (car pair) (cdr pair) t))
                 (list (cons dest-win src-buf)
                       (cons src-win dest-buf)))
         (error (throw 'except "Swap failed!")))
       (select-window dest-win t)
       (format "Swap window-buffers: %s <=> %s"
               (buffer-name src-buf) (buffer-name dest-buf))))))