DONE singe-function tangling and loading elisp from literate org-mode file [3/3]

lisp/org-babel-tangle.el

@@ -43,13 +43,26 @@ file.")
 org-mode formatted FILE.  This function will first export the
 source code using `org-babel-tangle' and then load the resulting
 file using `load-file'."
-  (mapc #'load-file (org-babel-tangle-file "emacs-lisp")))
+  (let ((loadable-file (first (org-babel-tangle-file file "emacs-lisp"))))
+    (message "loading %s" loadable-file)
+    (unless (file-exists-p loadable-file)
+      (error "can't load file that doesn't exist"))
+    (load-file loadable-file)
+    (message "loaded %s" loadable-file)))
 
 (defun org-babel-tangle-file (file &optional lang)
   "Extract the bodies of all source code blocks in FILE with
 `org-babel-tangle'.  Optional argument LANG can be used to limit
 the exported source code blocks by language."
-  (save-window-excursion (find-file file) (org-babel-tangle lang)))
+  (flet ((age (file)
+              (time-to-seconds
+               (time-subtract (current-time)
+                              (sixth (file-attributes file))))))
+    (let ((target-file (concat (file-name-sans-extension file) "."
+                               (second (assoc lang org-babel-tangle-langs)))))
+      (if (and lang (file-exists-p target-file) (> (age file) (age target-file)))
+          (list target-file)
+        (save-window-excursion (find-file file) (org-babel-tangle lang))))))
 
 (defun org-babel-tangle (&optional lang)
   "Extract the bodies of all source code blocks from the current

org-babel.org

@@ -199,34 +199,7 @@ would then be [[#sandbox][the sandbox]].
 #+end_src
 
 
-* Tasks [27/44]
-** TODO singe-function tangling and loading elisp from literate org-mode file [2/3]
-
-This function should tangle the org-mode file for elisp, and then call
-`load-file' on the resulting tangled file.
-
-#+srcname: test-loading-embedded-emacs-lisp
-#+begin_src emacs-lisp 
-  (org-babel-load-file "test-tangle.org")
-  (list test-tangle-loading test-tangle-advert)
-#+end_src
-
-*** DONE add optional language limiter to org-babel-tangle
-This should check to see if there is any need to re-export
-
-*** DONE ensure that org-babel-tangle returns the path to the tangled file(s)
-
-#+srcname: test-return-value-of-org-babel-tangle
-#+begin_src emacs-lisp :results replace
-  (mapcar #'file-name-nondirectory (org-babel-tangle-file "test-tangle.org" "emacs-lisp"))
-#+end_src
-
-#+resname:
-| "test-tangle.el" |
-
-*** TODO only tangle the file if it's actually necessary
-compare the ages of the files
-
+* Tasks [28/44]
 ** TODO support for working with =*Org Edit Src Example*= buffers [2/4]
 *** TODO optionally evaluate header references when we switch to =*Org Edit Src*= buffer
 That seems to imply that the header references need to be evaluated
@@ -870,6 +843,41 @@ $0
 [[file:snippets/org-mode/sb][sb -- snippet]]
 
 waiting for guidance from those more familiar with yasnippets
+** DONE singe-function tangling and loading elisp from literate org-mode file [3/3]
+
+This function should tangle the org-mode file for elisp, and then call
+`load-file' on the resulting tangled file.
+
+#+srcname: test-loading-embedded-emacs-lisp
+#+begin_src emacs-lisp :results replace
+  (setq test-tangle-advert nil)
+  (setq test-tangle-loading nil)
+  (setq results (list :before test-tangle-loading test-tangle-advert))
+  (org-babel-load-file "test-tangle.org")
+  (setq results (list (list :after test-tangle-loading test-tangle-advert) results))
+  (delete-file "test-tangle.el")
+  (reverse results)
+#+end_src
+
+#+resname: test-loading-embedded-emacs-lisp
+| :before | nil                 | nil                                                              |
+| :after  | "org-babel tangles" | "use org-babel-tangle for all your emacs initialization files!!" |
+
+*** DONE add optional language limiter to org-babel-tangle
+This should check to see if there is any need to re-export
+
+*** DONE ensure that org-babel-tangle returns the path to the tangled file(s)
+
+#+srcname: test-return-value-of-org-babel-tangle
+#+begin_src emacs-lisp :results replace
+  (mapcar #'file-name-nondirectory (org-babel-tangle-file "test-tangle.org" "emacs-lisp"))
+#+end_src
+
+#+resname:
+| "test-tangle.el" |
+
+*** DONE only tangle the file if it's actually necessary
+compare the ages of the files
 ** DONE add a function to jump to a source-block by name
    I've had an initial stab at that in org-babel-find-named-block
    (library-of-babel branch).

test-tangle.org

@@ -84,5 +84,4 @@ plus_two(holder)
 #+begin_src emacs-lisp 
   (setq test-tangle-loading "org-babel tangles")
   (setq test-tangle-advert "use org-babel-tangle for all your emacs initialization files!!")
-  (setq test-tangle-file-path (expand-file-name (buffer-file-name)))
 #+end_src