swap two windows

defuns.el

(require 'cl)

(defun swap-windows ()
 "If you have 2 windows, it swaps them."
 (interactive)
 (cond ((not (= (count-windows) 2))
        (message "You need exactly 2 windows to do this."))
       (t
        (let* ((w1 (first (window-list)))
               (w2 (second (window-list)))
               (b1 (window-buffer w1))
               (b2 (window-buffer w2))
               (s1 (window-start w1))
               (s2 (window-start w2)))
          (set-window-buffer w1 b2)
          (set-window-buffer w2 b1)
          (set-window-start w1 s2)
          (set-window-start w2 s1)))))