fixed to use common infrastructure, handle more cases, narrow/widen o…

…n entry/exit

slide-mode.el

@@ -13,21 +13,16 @@
 (defun slide-build-mode-map ()
   "Build the mode map for slide mode."
   (let  ((map (make-keymap)))
-    (define-key map "\C-n" 'next-slide)
+    (define-key map "\C-c\C-n" 'next-slide)
+    (define-key map "\C-c\C-p" 'previous-slide)
     map))
 
-;; define the mode
-(define-minor-mode slide-mode
-  "Toggle minor mode for display of slides."
-  nil " Slides" (slide-build-mode-map)
-  t)
-
-;; move to the next slide
-(defun next-slide ()
-  "Go to next slide."
-  (interactive)
-  (widen)
-  (if (re-search-forward "^\C-l$" (point-max) t)
+;; Actually display the current slide.
+;; Must be widened at entry,
+;; will be narrowed at exit.
+(defun display-slide ()
+  (setq here (point))
+  (if (re-search-backward "^\C-l$" (point-min) t)
       (beginning-of-line 2)
       (goto-char (point-min)))
   (setq start (point))
@@ -38,3 +33,35 @@
   (goto-char (point-min))
   (recenter)
   (goto-char (point-max)))
+
+;; Define the mode.
+;; When mode is activated,
+;; narrow on current slide.
+;; When mode is deactivated,
+;; widen.
+(define-minor-mode slide-mode
+  "Toggle minor mode for display of slides."
+  nil " Slides" (slide-build-mode-map)
+  (widen)
+  (if slide-mode
+      (display-slide)))
+
+;; move to the next slide
+(defun next-slide ()
+  "Go to next slide."
+  (interactive)
+  (widen)
+  (if (re-search-forward "^\C-l$" (point-max) t)
+      (progn
+	(beginning-of-line 2)
+	(display-slide))))
+
+;; move to the previous slide
+(defun previous-slide ()
+  "Go to previous slide."
+  (interactive)
+  (widen)
+  (if (re-search-backward "^\C-l$" (point-min) t)
+      (progn
+       (beginning-of-line nil)
+       (display-slide))))