Patch: Allow installation of file-local export filters

[Carsten Dominik <carsten.dominik@gmail.com>]

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Hi Nicolas,

please take a look at the attached patch - it shows what I am trying to do.
I think is is a nice way to tweak export on a file-local scope,
in a self-contained way, so that the file carries it special filters.

WDYT?


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diff --git a/lisp/ox.el b/lisp/ox.el
index 10354b2..f68dc78 100644
--- a/lisp/ox.el
+++ b/lisp/ox.el
@@ -2796,6 +2796,52 @@ Return the updated communication channel."
     ;; Return new communication channel.
     (org-combine-plists info plist)))
 
+(defun org-export-define-local-filters (filter-alist)
+  "Function to be used in an src block to install file-local export filters.
+The function takes an alist, where each element is a list of three items:
+
+1. The filter to be modified.  This should be a filter symbol like `XXX'
+   to indicate the filter variable `org-export-filter-XXX-functions'.
+
+2. The filter function to be installed in that variable.  This must be a
+   function or `lambda' form that accepts the usual three arguments for
+   filter function (string backend info).
+
+3. An optional REPLACE flag.  When t, the default value of the filter
+   variable will be discarded and the local filter will be the only
+   one in that filter variable.  When nil, the new filter will be added
+   to the existing ones.
+
+Here is an example that will install filters to remove brackets from
+time stamps, and to eliminate strike-through text.
+
+   #+begin_src emacs-lisp :exports results :results none
+     (org-export-define-local-filters
+      '((timestamp
+         (lambda (timestamp backend info)
+           \"Remove brackets from timestamp.\"
+           (when (org-export-derived-backend-p backend 'html)
+             (replace-regexp-in-string \"&[l]t;\\|[][]\" \"\" timestamp))))
+        (strike-through
+         (lambda (s backend info)
+           \"Remove strike-through text\"
+           \"\")
+         replace)))
+   #+end_src"
+  (let (next var filter replace)
+    (while (setq next (pop filter-alist))
+      (setq var (car next)
+	    filter (nth 1 next)
+	    replace (nth 2 next))
+      (setq var (intern (concat "org-export-filter-" (symbol-name var)
+				"-functions")))
+      (make-local-variable var)
+      (if replace
+	  (if filter
+	      (set var (list filter))
+	    (set var nil))
+	(if filter
+	    (add-to-list var filter))))))
 
 \f
 ;;; Core functions
@@ -3346,11 +3392,15 @@ file should have."
 			(insert (make-string offset ?*)))))))))))
     (org-element-normalize-string (buffer-string))))
 
+(defvar org-export-executing-babel-code-for-export nil
+  "Flag to be bound using `let'")
+
 (defun org-export-execute-babel-code ()
   "Execute every Babel code in the visible part of current buffer."
   ;; Get a pristine copy of current buffer so Babel references can be
   ;; properly resolved.
-  (let ((reference (org-export-copy-buffer)))
+  (let ((reference (org-export-copy-buffer))
+	(org-export-executing-babel-code-for-export t))
     (unwind-protect (let ((org-current-export-file reference))
 		      (org-babel-exp-process-buffer))
       (kill-buffer reference))))
@@ -6213,7 +6263,6 @@ options as CDR."
      (t (org-export--dispatch-ui options key expertp)))))
 
 
-
 (provide 'ox)
 
 ;; Local variables:

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On 22.9.2013, at 14:26, Carsten Dominik <carsten.dominik@gmail.com> wrote:

> 
> On 22.9.2013, at 14:22, Nicolas Goaziou <n.goaziou@gmail.com> wrote:
> 
>> Hello,
>> 
>> Carsten Dominik <carsten.dominik@gmail.com> writes:
>> 
>>> I am trying to write a function that will only run if it is called
>>> during the evaluation of babel code during export, so basically during
>>> `org-export-execute-babel code'. Do you know if there is a way to
>>> detect that this is the case,
>> 
>> There isn't.
>> 
>>> or should I introduce a flag that is set by
>>> `org-export-execute-babel-code'?
>> 
>> This may be dangerous. Introducing such a flag means that Babel results
>> may be different when exporting and when evaluating a block.
> 
> This is exactly the point.  I want to be able to create local variables
> and change filter lists during export, while interactive evaluation should
> not create local variables in the Org mode buffer.  I do not plan to
> advertise this flag, but to use it in one very specific function.
> 
> Regards
> 
> - Carsten
>> 
>> 
>> Regards,
>> 
>> -- 
>> Nicolas Goaziou
> 


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