Pre Process Org mode export

Question

This is the emacs side of a question I asked on the Latex SE.

This other emacs question is also related but for now I am assuming its not an issue

Short version

I want the best of two worlds:

• The org-tab behavior of *-ed headlines
• The Latex typesetting nuance of \newtheorem applied on these headlines

IOW I want headlines -- maybe slightly doctored -- to behave as headlines in emacs; and to export as math in Latex. Except that instead of Equation Lemma Theorem etc I want Law Fact Action

This table summarizes

Idea	Emacs code	Latex Behavior
Law	* Text :L:	$\odot$ Law nn Text
Fact	* Text :F:	$\boxdot$ Fact nn Text
Action	* Text :A:	\checkmark Action nn Text

nn's are the auto-numbering of org-latex as it normally works

Longer Version

Say I have a heading like

* Recursion before Iteration  :L:

I want it to become on the latex side (something like)

\textbf{$\odot$ Law nn. Recursion before Iteration}

---

One thing I (guess) I want is a full scale preprocessor of org-export

So something like a sed modification on the buffer before export

---

Added Later

After writing the above I found this question with this answer.

That gives me greater clarity.

So there is the function org-export-ignore-headlines in ox-extra.el

How do I change it so that on Latex export

* Lorem Ipsum  :L:

is converted to

#+BEGIN_LAW
Lorem Ipsum
#+END_LAW

[Assume that a suitable law environment has been created in the style file using newtheorem

---

In response to TMar

No your attempt does not work.

If I give:

* A
** Recursion before Iteration                :LAW:
Lorem Ipsum

I get

\begin{document}

\tableofcontents

\#+BEGIN\textsubscript{LAW} 

\section{A}
\label{sec:org196f793}
\#+END\textsubscript{LAW} 

Recursion before Iteration                :LAW:
Lorem Ipsum
\end{document}

IOW

• sequencing of fragments is wrong
• timing is wrong -- its happening after begin blocks are processed

The second point can be obviated by simply replacing the #+BEGIN_LAW by \begin{law}. But what should go in the block is going outside the block.

In answer to NickD

Two alternatives

1. The simpler one

   *** Recursion before Iteration :L:
   # nothing allowed here inside
   

   becomes

   #+begin_law
   Recursion before Iteration
   #+end_law
   

2. More fiddly but hopefully not too hairy! Assume that :ignore: headlines are ignored though their contents are exported according to org-export-ignore headlines. So

   *** Recursion before Iteration  :L:
   Lorem ipsum etc
   

   becomes

   *** Dummy :ignore:
   #+begin_law
   Recursion before Iteration
   #+end_law
   Lorem Ipsum etc
   

Answer 1

Another approach is, for example, to have a pre-processing using org-export-before-parsing-hook. Here is a small code with this idea.

(defun my-modify-headline(text1 text2)
  "Modify the headline"
  (interactive)
  (message "modifying headlines")
  (save-excursion
    (goto-char (point-min)) 
    (save-match-data
      ;; For each heading, do
      (while (re-search-forward org-heading-regexp nil t)
    ;; test that the tag LAW is in the headline. 
       (if  (member "LAW" (org-get-tags))
    ;; remove headline format (e.g. remove the stars)
       (progn (org-toggle-heading)
          (save-excursion
            ;; add line before
            (end-of-line 0)
            (open-line 1)
        (forward-line 1) 
            ;; add text1
            (insert text1)
          )
          (save-excursion
            ;; add line after
          (end-of-line)
          (open-line 1)
          (forward-line 1) 
          ;; add text2
          (insert text2))))))))
  
(defun insert-beginning-end (backend)
  " insert beginning and end"
  (my-modify-headline  "\#+BEGIN_LAW \n"  "\#+END_LAW \n"))

(add-hook 'org-export-before-parsing-hook #'insert-beginning-end)