Emacs: toggle between split windows and a single window

emacs-window-toggle.el

;; Toggle between split windows and a single window
(defun toggle-windows-split()
  "Switch back and forth between one window and whatever split of windows we might have in the frame. The idea is to maximize the current buffer, while being able to go back to the previous split of windows in the frame simply by calling this command again."
  (interactive)
  (if (not (window-minibuffer-p (selected-window)))
      (progn
        (if (< 1 (count-windows))
            (progn
              (window-configuration-to-register ?u)
              (delete-other-windows))
          (jump-to-register ?u))))
  (my-iswitchb-close))

(define-key global-map (kbd "C-|") 'toggle-windows-split)


;; Note: you may also need to define the my-iswitchb-close function 
;; created by Ignacio as well: http://emacswiki.org/emacs/IgnacioPazPosse
(defun my-iswitchb-close()
 "Open iswitchb or, if in minibuffer go to next match. Handy way to cycle through the ring."
 (interactive)
 (if (window-minibuffer-p (selected-window))
    (keyboard-escape-quit)))

my-iswitchb-close is not defined. It should be defined or omitted. Thanks for the code!

Done. Good catch!