Re: [Orgmode] Re: org-babel matlab example

[Darlan Cavalcante Moreira]

Hello Dan,

I wasn't sure if I had suggested this before or not, but now I remember
that it was in a thread about python.

I have only used org babel with python and octave and I don't know how this
would translate to other languages, but I think it makes sense in languages
that you can work with scripts. Let me elaborate.

Suppose I have the two code snippets below:
--8<---------------cut here---------------start------------->8---
#+begin_src python :results value
  from numpy import arange
  print "I don't want to see this"
  a=arange(1,10)
  a+2 # Only this as the last statement is not enough
  return a+2 # We need to add return a+2
#+end_src
--8<---------------cut here---------------end--------------->8---
--8<---------------cut here---------------start------------->8---
#+begin_src octave :results value
  disp 'I dont want to see this'
  a=1:10
  b=a+2 # Only this is not enough because ans was never set
  ans = b
#+end_src
--8<---------------cut here---------------end--------------->8---

In both cases I want to see the value of a variable after executing a
script and not what the script prints to the screen. From babel
documentation I can see that I need the "functional mode" with the header
argument :results value. However, in the python example I need to add a
"return" statement even though I didn't declare a python function in the
code (this is invalid code if I tangle it).

Also, in the octave example if the 'ans' variable was set before to some
value, babel would show it after execution, instead of the value of the
last statement as one could think.

Therefore, the suggestion is that since babel is implicitly declaring a
function (with a def in python, for example), it is more natural that it
also "write" the return statement which I could set with a ":return" header
argument and not in the language code.

The two snippets would become
--8<---------------cut here---------------start------------->8---
#+begin_src python :return b
  from numpy import arange
  print "I don't want to see this"
  a=arange(1,10)
  b=a+2
#+end_src
--8<---------------cut here---------------end--------------->8---
--8<---------------cut here---------------start------------->8---
#+begin_src octave :return b
  disp 'I dont want to see this'
  a=1:10
  b=a+2
#+end_src
--8<---------------cut here---------------end--------------->8---
where the ":results" argument would not be necessary to specify "functional
mode".

--
Darlan

At Tue, 14 Sep 2010 16:40:48 +0100,
Dan Davison wrote:
> 
> Darlan Cavalcante Moreira <address@hidden> writes:
> 
> > Can I leave a suggestion here?
> > Maybe a header argument
> > ,----
> > | :return variableName
> > `----
> > could be interesting in org babel. This would make babel behavior more
> > uniform in all supported languages and avoid the necessity of adding code
> > "only to make babel work".
> 
> Hi Darlan,
> 
> Thanks (and sorry if you've made this suggestion previously, which I
> seem to recall). I can see that this would be particularly natural for
> matlab/octave in which (aIui) function definitions require specifying
> the name of the variable whose value is to be returned. In other
> languages which I've encountered, return values are determined by either
> "return" statements, or the value of the last statement in the function,
> or both of these mechanisms. So if we were to apply your suggestion to
> all languages, one could argue that it would permit un-natural code in
> languages other than matlab/octave. As you say, we do want things to be
> uniform across languages, but perhaps there is an argument for
> restricting your suggestion to matlab/octave?
> 
> Dan
> 
> >
> > --
> > Darlan
> >
> > At Sun, 12 Sep 2010 08:45:40 +0100 (BST),
> > etimecowboy <address@hidden> wrote:
> >> 
> >> From: Dan Davison <address@hidden>
> >> Subject: Re: org-babel matlab example
> >> Date: Sat, 11 Sep 2010 12:23:17 -0400
> >> 
> >> > Dan Davison <address@hidden> writes:
> >> > 
> >> >> etimecowboy <address@hidden> writes:
> >> >>
> >> >>> Hi everybody,
> >> >>>
> >> >>> I am learning to use org-babel to evaluate in-line Matlab code block,
> >> >>> but I cannot make it works when I press the "C-c C-c", nor "C-c C-v
> >> >>> e".
> >> >>
> >> >> What happens when you try C-c C-c or C-c C-v e ? There is an issue with
> >> >> matlab and octave: they return the value of the last /unassigned/
> >> >> computation
> >> > 
> >> > A better way to say this is: they return the value of the special
> >> > variable "ans". So whatever you do, at the end of the block you need to
> >> > ensure that "ans" has the value that you want returned.
> >> > 
> >> > I've updated the Worg page on Matlab and Octave:
> >> > 
> >> > http://orgmode.org/worg/org-contrib/babel/languages/ob-doc-octave-matlab.php
> >> > 
> >> > Dan
> >> > 
> >> > 
> >> >>, so simply ending the code block with a variable name "x" is
> >> >> not enough. Could you try one of the following schemes please, and let
> >> >> us know if that solves it:
> >> >>
> >> >> #+begin_src matlab :exports results
> >> >> n = [1:10];
> >> >> x = 5*n+4;
> >> >> ans = x
> >> >> #+end_src
> >> >>
> >> >> #+begin_src matlab :exports results
> >> >> n = [1:10];
> >> >> x = 5*n+4;
> >> >> x + 0
> >> >> #+end_src
> >> >>
> >> >>
> >> >>> The export of code works, but the results was not there. My in-line 
> >> >>> code is like this:
> >> >>
> >> >> There was a little typo in your original block: the keyword is
> >> >> ":exports" with an s.
> >> >>
> >> >> Dan
> >> >>
> >> >>>
> >> >>> #+begin_src matlab :export results
> >> >>> n = [1:10];
> >> >>> x = 5*n+4;
> >> >>> x
> >> >>> #+end_src
> >> >>>
> >> >>> Is there someone can provide me a working example? Thanks a lot.
> >> >>>
> >> >>>
> >> >>> -----------------------------
> >> >>>
> >> >>> address@hidden
> >> >>>
> >> >>>       _.,----,._
> >> >>>     .:'        `:.
> >> >>>   .'              `.
> >> >>>  .'                `.
> >> >>>  :                  :
> >> >>>  `    .'`':'`'`/    '
> >> >>>   `.   \  |   /   ,'
> >> >>>     \   \ |  /   /
> >> >>>      `\_..,,.._/'
> >> >>>       {`'-,_`'-}
> >> >>>       {`'-,_`'-}
> >> >>>       {`'-,_`'-}
> >> >>>        `YXXXXY'
> >> >>>          ~^^~
> >> >>>
> >> >>> _______________________________________________
> >> >>> Emacs-orgmode mailing list
> >> >>> Please use `Reply All' to send replies to the list.
> >> >>> address@hidden
> >> >>> http://lists.gnu.org/mailman/listinfo/emacs-orgmode
> >> >>
> >> >> _______________________________________________
> >> >> Emacs-orgmode mailing list
> >> >> Please use `Reply All' to send replies to the list.
> >> >> address@hidden
> >> >> http://lists.gnu.org/mailman/listinfo/emacs-orgmode
> >> 
> >> Dear Dan,
> >> 
> >> I have checked the Worg page you updated and tried your example. It works! 
> >> The ans variable is the secret! Thanks a lot. I suggest org should provide 
> >> some examples in its user's guide, not only on the topic of Babel but also 
> >> Table, Hyperlink, Picture, and etc.
> >> 
> >> -----------------------------
> >> 
> >> address@hidden
> >> 
> >>       _.,----,._
> >>     .:'        `:.
> >>   .'              `.
> >>  .'                `.
> >>  :                  :
> >>  `    .'`':'`'`/    '
> >>   `.   \  |   /   ,'
> >>     \   \ |  /   /
> >>      `\_..,,.._/'
> >>       {`'-,_`'-}
> >>       {`'-,_`'-}
> >>       {`'-,_`'-}
> >>        `YXXXXY'
> >>          ~^^~
> >> 
> >> _______________________________________________
> >> Emacs-orgmode mailing list
> >> Please use `Reply All' to send replies to the list.
> >> address@hidden
> >> http://lists.gnu.org/mailman/listinfo/emacs-orgmode