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 '()".

#+name: unset-colnames-example-input
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |

** Having no =:colnames= header argument (case 1)

I understand that the following example does have =:colnames= set to =yes=: it 
is
neither unset nor changed on the code block specification.

#+begin_src emacs-lisp :var data=unset-colnames-example-input
  data
#+end_src

#+results:
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |

Hence, this result is what is expected.

** Using =:colnames no= header argument (case 2)

#+begin_src emacs-lisp :var data=unset-colnames-example-input :colnames no
  data
#+end_src

#+results:
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |

Here, I still don't understand why I do see the table header line: I did
change the default =:colnames yes= specification to =:colnames no= on the code
block. I did override the default value. Why is the =no= argument not
respected?

** Using =:colnames yes= header argument (case 3)

#+begin_src emacs-lisp :var data=unset-colnames-example-input :colnames yes
  data
#+end_src

#+results:
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |

Here, the =:colnames yes= specification is simply redundant to what's specified
for the emacs-lisp language. In all cases, the results is what is should be.

** Using =:colnames nil= header argument (case 5)

#+begin_src emacs-lisp :var data=unset-colnames-example-input :colnames nil
  data
#+end_src

#+results:
| a | b |
|---+---|
| 1 | 2 |
| 3 | 4 |

As written in my previous post, =:colnames nil= is equivalent to =:colnames yes=
in Emacs Lisp, R and sh code blocks -- at least.

(Still) not clear to me -- sorry to be stubborn.

** Using =:colnames ()= header argument (case 6)

As you told me, to "unset" the =:colnames yes= header argument, we must use:

#+begin_src emacs-lisp :var data=unset-colnames-example-input :colnames ()
  data
#+end_src

#+results:
| 1 | 2 |
| 3 | 4 |

That does work.

** Using =:colnames ()= header argument (case 7)

So does the quoted empty list version...

#+begin_src emacs-lisp :var data=unset-colnames-example-input :colnames '()
  data
#+end_src

#+results:
| 1 | 2 |
| 3 | 4 |

What is still unclear to me as well, is why =()= and =nil= aren't the same from
Babel's point of view?

Best regards,
  Seb

-- 
Sebastien Vauban