fold-able (hide-able) code blocks

Using org-cycle, just hit [TAB] with the point on the =#+BEGIN_SRC=
  line of a source-code block.

litorgy/init.el

@@ -33,6 +33,7 @@
 (load "htmlize.el") ;; other versions of htmlize can cause export problems
 (require 'litorgy)
 (require 'litorgy-ref)
+(require 'litorgy-ui)
 
 ;; language specific files
 (require 'litorgy-script)

litorgy/litorgy-ui.el

@@ -0,0 +1,62 @@
+;;; litorgy-ui.el --- UI elements for litorgy
+
+;; Copyright (C) 2009 Eric Schulte, Dan Davison, Austin F. Frank
+
+;; Author: Eric Schulte, Dan Davison, Austin F. Frank
+;; Keywords: literate programming, reproducible research
+;; Homepage: http://orgmode.org
+;; Version: 0.01
+
+;;; License:
+
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 3, or (at your option)
+;; any later version.
+;;
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+;;
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+;; Boston, MA 02110-1301, USA.
+
+;;; Commentary:
+
+;; UI elements of litorgy
+;; - code folding
+;; - marking working code blocks
+
+;;; Code:
+(require 'litorgy)
+
+(defadvice org-cycle (around litorgy-ui-org-cycle-src-block activate)
+  "Intercept calls to org-cycle to toggle the visibility of a source code block."
+  (if (save-excursion
+          (beginning-of-line 1)
+          (looking-at litorgy-src-block-regexp))
+      (litorgy-ui-src-block-cycle)
+    ad-do-it))
+
+(defun litorgy-ui-src-block-cycle ()
+  "Cycle the visibility of the current source code block"
+  (interactive)
+  ;; should really do this once in an (org-mode hook)
+  (add-to-invisibility-spec '(litorgy-ui . t))
+  (save-excursion
+    (beginning-of-line)
+    (if (re-search-forward litorgy-src-block-regexp nil t)
+        (let ((start (- (match-beginning 4) 1)) ;; beginning of body
+              (end (match-end 0))) ;; end of entire body
+          (if (memq t (mapcar (lambda (overlay)
+                                (eq (overlay-get overlay 'invisible) 'litorgy-ui))
+                              (overlays-at start)))
+              (remove-overlays start end 'invisible 'litorgy-ui)
+            (overlay-put (make-overlay start end) 'invisible 'litorgy-ui)))
+      (error "not looking at source code block"))))
+
+(provide 'litorgy-ui)
+;;; litorgy-ui ends here