Re: [PATCH] Prevent overwriting of output files from babel calls with nil result

[Aaron Ecay <aaronecay@gmail.com>]

Hi Éibhear,

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 ‘params’, 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’t predict what the
result would be of making it return the symbol nil instead of the string
“nil.”  (Though for the sake of consistency it ought to allow 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
| 
| #+RESULTS: dot-code
| : "your dot code will appear here"
| 
| #+begin_src dot :file foo.png :var code=dot-code()
| $code
| #+end_src
|
| #+RESULTS:
| [[file:foo.png]]
`----

Hope this helps,

-- 
Aaron Ecay