From mboxrd@z Thu Jan  1 00:00:00 1970
From: Aaron Ecay <aaronecay@gmail.com>
Subject: Re: [PATCH] Prevent overwriting of output files from babel calls
 with nil result
Date: Thu, 29 Oct 2015 19:59:58 +0000
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To: =?utf-8?Q?=C3=89ibhear?= <eibhear.geo@gmail.com>, Org Mode <emacs-orgmode@gnu.org>

Hi =C3=89ibhear,

Thanks for sending the example.  I think it is not expected to work
going forward because the lisp block relies on being able to pick up the
value of =E2=80=98params=E2=80=99, which will not be possible now that org =
is moving to
lexical binding.  In general, org-babel-execute:foo are internal
functions, so trying to trick them int working properly in an elisp code
block is a bad idea.

The emacs-lisp babel backend is special, so I can=E2=80=99t predict what the
result would be of making it return the symbol nil instead of the string
=E2=80=9Cnil.=E2=80=9D  (Though for the sake of consistency it ought to all=
ow nil symbol
returns.)

On the balance, I recommend you do something like the following, using
two code blocks (untested):

,----
| #+name: dot-code
| #+begin_src emacs-lisp :results verbatim
| (generate-dot-code)
| #+end_src
|=20
| #+RESULTS: dot-code
| : "your dot code will appear here"
|=20
| #+begin_src dot :file foo.png :var code=3Ddot-code()
| $code
| #+end_src
|
| #+RESULTS:
| [[file:foo.png]]
`----

Hope this helps,

--=20
Aaron Ecay