[O] Switch for exported file types when evaluating code blocks

[Brett Viren]

Hi,

I'm hitting on an old theme in a new way here.  

I want graphics files which are exported by evaluated code blocks to be
generated in a format best suited to their intended use.  For HTML I
want either PNG or SVG.  For LaTeX/PDF I almost always want PDF.  For
inline viewing in emacs I want either PNG or SVG.

To that end I went a'googling and found this idea:

  http://orgmode.org/worg/org-contrib/babel/languages/ob-doc-LaTeX.html#sec-4-3

It doesn't work with my copies[1] of emacs and org-mode but I was able
to adapt it.  I suck at elisp so this is probably more an accomplishment
to me than it appears to most of you!

In any case, here is a short org document based on the one I found above
in worg which shows what I ended up with:


* COMMENT setup
#+begin_src emacs-lisp :results silent
  (defmacro by-backend (&rest body)
    `(case (if (boundp 'backend) backend nil) ,@body))
#+end_src

* A graph
#+header: :file (by-backend (html "graph.png") (latex "graph.pdf") (t 
"graph.svg"))
#+header: :export results
#+begin_src dot
digraph Name {
        tail -> head;
}
#+end_src


I think the real learning experience for me was that I could put lisp
directly in a header like this!  Now, I just gotta learn elisp
better....

Also, I'd certainly be interested to hear of any better ways to
accomplish this.

Thanks,
-Brett.


[1] The versions I'm using are

 - Org-mode version 8.0.3 (8.0.3-elpa @ 
/home/bviren/.emacs.d/elpa/org-20130514/)

 - GNU Emacs 24.1.1 (i486-pc-linux-gnu, GTK+ Version 2.24.10) of 2012-07-20 on 
murphy, modified by Debian

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