From: "Sebastien Vauban" <wxhgmqzgwmuf-geNee64TY+gS+FvcfC7Uqw@public.gmane.org>
To: emacs-orgmode-mXXj517/zsQ@public.gmane.org
Subject: Re: [babel] Bugs for Emacs Lisp code blocks
Date: Tue, 09 Apr 2013 10:13:59 +0200 [thread overview]
Message-ID: <86wqsc6rzs.fsf@somewhere.org> (raw)
In-Reply-To: 87a9p8zq7d.fsf@gmail.com
Hi Eric,
Eric Schulte wrote:
> "Sebastien Vauban" <wxhgmqzgwmuf-geNee64TY+gS+FvcfC7Uqw@public.gmane.org> writes:
>> Eric Schulte wrote:
>>> "Sebastien Vauban" <wxhgmqzgwmuf-geNee64TY+gS+FvcfC7Uqw@public.gmane.org> 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.
I don't share your view about this last statement.
** Input table
#+name: unset-colnames-example-input
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |
** Having no =:colnames= header argument (case 1)
Same results for R and sh code blocks (first good news ;-)) -- I'm avoiding,
on purpose, testing with Emacs Lisp...
#+begin_src R :var data=unset-colnames-example-input
data
#+end_src
#+results:
| 1 | 2 |
| 3 | 4 |
#+begin_src sh :var data=unset-colnames-example-input
echo "$data"
#+end_src
#+results:
| 1 | 2 |
| 3 | 4 |
** Using =:colnames nil= header argument (case 5)
Once again, R and sh blocks do produce the same results...
#+begin_src R :var data=unset-colnames-example-input :colnames nil
data
#+end_src
#+results:
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |
#+begin_src sh :var data=unset-colnames-example-input :colnames nil
echo "$data"
#+end_src
#+results:
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |
... but they are _not_ equivalent to the "no header argument" (case 1).
** Using =:colnames yes= header argument (case 3)
On the contrary, case 5 is equivalent to the case 3: same results as
":colnames yes".
#+begin_src R :var data=unset-colnames-example-input :colnames yes
data
#+end_src
#+results:
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |
#+begin_src sh :var data=unset-colnames-example-input :colnames yes
echo "$data"
#+end_src
#+results:
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |
>> 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").
Not sure to find what you want me to read in that page...
> We could add nil as a special exception, but that might be surprising to
> some people.
As far as the Lisp interpreter is concerned, () and nil are the same, right?
Then, why do you talk of adding a special exception? Maybe, I don't
understand your point because I'm missing the context info you wanted me to
read just above?
>> 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.
>
> ** 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. [...]
> 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 |
This is clear -- thanks! -- but it does not unset the header argument as long
as case 1 and 5 are not the same in the above given example (for R and sh
blocks).
Best regards,
Seb
--
Sebastien Vauban
next prev parent reply other threads:[~2013-04-09 8:13 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
2013-04-09 8:13 ` Sebastien Vauban [this message]
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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