From: Eric Schulte <schulte.eric@gmail.com>
To: Sebastien Vauban <wxhgmqzgwmuf@spammotel.com>
Cc: emacs-orgmode@gnu.org
Subject: Re: [babel] Bugs for Emacs Lisp code blocks
Date: Mon, 08 Apr 2013 15:07:34 -0600 [thread overview]
Message-ID: <87a9p8zq7d.fsf@gmail.com> (raw)
In-Reply-To: <86ehek93w7.fsf@somewhere.org> (Sebastien Vauban's message of "Mon, 08 Apr 2013 22:14:00 +0200")
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"Sebastien Vauban" <wxhgmqzgwmuf@spammotel.com> writes:
> Hi Eric,
>
> Eric Schulte wrote:
>> "Sebastien Vauban" <wxhgmqzgwmuf@spammotel.com> 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?
>
Almost, values 1 (none) and 5 (nil) are the same.
>
> 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?
>
See "Emacs Lisp evaluation of variables" in (info "(org)var"). We could
add nil as a special exception, but that might be surprising to some
people.
>
> 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?
>
Whenever you want to "unset" a header argument, which has a value set at
some higher level.
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** unset the colnames header argument
#+name: unset-colnames-example-input
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |
Unlike most code blocks, Emacs Lisp has colnames set to "yes" in its
default header arguments.
#+begin_src emacs-lisp
org-babel-default-header-args:emacs-lisp
#+end_src
#+RESULTS:
| (:hlines . yes) | (:colnames . no) |
As a result it has the following behavior by default.
#+begin_src emacs-lisp :var data=unset-colnames-example-input
data
#+end_src
#+RESULTS:
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |
If we wanted to unset this value, we could do the following.
#+begin_src emacs-lisp :var data=unset-colnames-example-input :colnames ()
data
#+end_src
#+RESULTS:
| 1 | 2 |
| 3 | 4 |
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Cheers,
>
> Best regards,
> Seb
--
Eric Schulte
http://cs.unm.edu/~eschulte
next prev parent reply other threads:[~2013-04-08 21:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-06 15:44 [babel] Bugs for Emacs Lisp code blocks Sebastien Vauban
2013-04-07 13:29 ` Eric Schulte
2013-04-07 15:47 ` Sebastien Vauban
2013-04-07 19:42 ` Eric Schulte
2013-04-08 20:14 ` Sebastien Vauban
2013-04-08 21:07 ` Eric Schulte [this message]
2013-04-09 8:13 ` Sebastien Vauban
2013-04-12 22:03 ` Eric Schulte
2013-04-15 13:46 ` Sebastien Vauban
2013-04-09 19:46 ` Sebastien Vauban
2013-04-10 7:54 ` Sebastien Vauban
2013-04-12 22:10 ` Eric Schulte
2013-04-15 14:09 ` Sebastien Vauban
2013-04-15 15:26 ` Eric Schulte
2013-04-12 22:09 ` Eric Schulte
2013-04-15 14:04 ` Sebastien Vauban
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