Re: [O] [babel] Bugs for Emacs Lisp code blocks

[Sebastien Vauban]

Hi Eric,

Eric Schulte wrote:
> "Sebastien Vauban" <address@hidden> writes:
>> Eric Schulte wrote:
>>> Emacs Lisp is an exception in terms of colname processing, it has default
>>> header arguments set to pass column names through to the code block, where
>>> the processing may be done trivially in Emacs Lisp.
>>
>> OK, but I don't understand the precedence of header arguments. I thought
>> that a header argument given on the code block preempted all the other
>> values (system-wide default for all languages, language defaults, file-wide
>> arguments, and subtree arguments).
>>
>> Why isn't this true here as well?
>
> That is what is happening here, although combinations of :hlines and
> :colnames can be tricky. Especially weird, is that if you want to *unset* a
> header argument which is set at a higher level, you need to set it to '(),
> as in ":colnames '()".

Much clearer, but not yet crystal-clear for me...

Let me explain. AFAICT, there were 5 possibles values of the ":colnames"
header argument:

- no header argument :: (default for all languages but Emacs Lisp)
- ":colnames no" :: (default for Emacs Lisp code blocks)
- ":colnames yes" :: Tells Org Babel that your first row contains column
  names.
- ":colnames <LIST>" :: Specifies to use <LIST> as column names.
- ":colnames nil" :: Same as ":colnames yes".

Right?

Now, indeed, your trick with ":colnames '()" (or even ":colnames ()"...) does
work well for Emacs-Lisp...

Though, I thought that "()" was equivalent to "nil", but it seems not to be
the case, then. Is it because of some sort of type coercion, that would
convert nil as a string or something along such lines?

Extra question: when do we have to use such a trick?  When the value can be a
list of things?  If yes, why are you talking of ":hlines" -- there is no list
argument there?

Best regards,
  Seb

-- 
Sebastien Vauban