+;;;; Helpful functions for enabling and disabling scroll bars.
+
+(defvar scroll-bar-mode)
+
+(defvar scroll-bar-mode-explicit nil
+ "Non-nil means `set-scroll-bar-mode' should really do something.
+This is nil while loading `scroll-bar.el', and t afterward.")
+
+(defun set-scroll-bar-mode-1 (ignore value)
+ (set-scroll-bar-mode value))
+
+(defun set-scroll-bar-mode (value)
+ "Set `scroll-bar-mode' to VALUE and put the new value into effect."
+ (setq scroll-bar-mode value)
+
+ (when scroll-bar-mode-explicit
+ ;; Apply it to default-frame-alist.
+ (let ((parameter (assq 'vertical-scroll-bars default-frame-alist)))
+ (if (consp parameter)
+ (setcdr parameter scroll-bar-mode)
+ (setq default-frame-alist
+ (cons (cons 'vertical-scroll-bars scroll-bar-mode)
+ default-frame-alist))))
+
+ ;; Apply it to existing frames.
+ (let ((frames (frame-list)))
+ (while frames
+ (modify-frame-parameters
+ (car frames)
+ (list (cons 'vertical-scroll-bars scroll-bar-mode)))
+ (setq frames (cdr frames))))))
+
+(defcustom scroll-bar-mode
+ (if (eq system-type 'windows-nt) 'right 'left)
+ "*Specify whether to have vertical scroll bars, and on which side.
+Possible values are nil (no scroll bars), `left' (scroll bars on left)
+and `right' (scroll bars on right).
+To set this variable in a Lisp program, use `set-scroll-bar-mode'
+to make it take real effect.
+Setting the variable with a customization buffer also takes effect."
+ :type '(choice (const :tag "none (nil)")
+ (const left)
+ (const right))
+ :group 'frames
+ :set 'set-scroll-bar-mode-1)
+
+;; We just set scroll-bar-mode, but that was the default.
+;; If it is set again, that is for real.
+(setq scroll-bar-mode-explicit t)
+
+(defun scroll-bar-mode (&optional flag)
+ "Toggle display of vertical scroll bars on all frames.
+This command applies to all frames that exist and frames to be
+created in the future.
+With a numeric argument, if the argument is negative,
+turn off scroll bars; otherwise, turn on scroll bars."
+ (interactive "P")
+ (if flag (setq flag (prefix-numeric-value flag)))
+
+ ;; Tweedle the variable according to the argument.
+ (set-scroll-bar-mode (if (null flag) (not scroll-bar-mode)
+ (and (or (not (numberp flag)) (>= flag 0))
+ (if (eq system-type 'windows-nt) 'right 'left)))))
+
+(defun toggle-scroll-bar (arg)
+ "Toggle whether or not the selected frame has vertical scroll bars.
+With arg, turn vertical scroll bars on if and only if arg is positive.
+The variable `scroll-bar-mode' controls which side the scroll bars are on
+when they are turned on; if it is nil, they go on the left."
+ (interactive "P")
+ (if (null arg)
+ (setq arg
+ (if (cdr (assq 'vertical-scroll-bars
+ (frame-parameters (selected-frame))))
+ -1 1))
+ (setq arg (prefix-numeric-value arg)))
+ (modify-frame-parameters
+ (selected-frame)
+ (list (cons 'vertical-scroll-bars
+ (if (> arg 0)
+ (or scroll-bar-mode
+ (if (eq system-type 'windows-nt) 'right 'left)))))))
+
+(defun toggle-horizontal-scroll-bar (arg)
+ "Toggle whether or not the selected frame has horizontal scroll bars.
+With arg, turn horizontal scroll bars on if and only if arg is positive.
+Horizontal scroll bars aren't implemented yet."
+ (interactive "P")
+ (error "Horizontal scroll bars aren't implemented yet"))
+\f
+;;;; Buffer navigation using the scroll bar.