evaluation of perl in babel

[D M German <dmg@uvic.ca>]

Hi Everybody,

I looked a bit more onto the way that perl is evaluated. I know the
support of perl is minor. I understand that, so please, don't see this
message as a complaint, so this is more for discussion and potential
improvements of the Perl support in Babel.

One of the things I have noticed is that the way that Babel handles the
results coming from the code is not the best.

Let me elaborate:

At the bottom you will find a set of test that stress the different
:results types.

There are some bugs. For example, the interpretation of :results table,
vector and list.

But I think the main problem comes from the way that Babel expects the
result. In Babel, and except for :results output, the last expression in
perl is considered the input to the results. This is implementing by
saving the last expression into a variable, and printing each value
separated by a "\n" (including the last). So basically, org takes the
last expression, and outputs them to the babel input file one per line.

This places some constraints. First, it is not currently capable of
dealing with two dimensional arrays. Second, it makes it hard to create
complex output (such as HTML or LaTeX), and third, it is hard to debug
without first printing the value of the array (this output would be lost
during the evaluation, so it would have be debugged outside org).

I feel that a better approach is to use std output as the default input
to any of these :results types, and then try to parse them into the
corresponding :results types. This will allow the creation of HTML and
LaTeX from perl (which the current implementation does not allow).

So recapitulating, my suggestion is that perl should use STDOUT as the
output of the snippet in any :results type, rather than the result of
the last expression.

I know this will break backwards compatibility. One solution is to keep
the current src perl and add a new perl_stdout mode (or something like
that) that implements this.

--dmg



----------------------------------------------------------------------
#+begin_src perl :results output 
print "Test\n";
(1, 2)
#+end_src

#+RESULTS:
: Test

#+name: t_output_raw
#+begin_src perl :results raw 
print "Test\n";
(1, 2)
#+end_src

#+RESULTS: t_output_raw
1
2

#+name: t_output_table
#+begin_src perl :results table
print "Test\n";
(1, 2)
#+end_src

#+RESULTS: t_output_table
| 1\n2\n |

#+name: t_output_vector
#+begin_src perl :results vector
print "Test\n";
(1, 2)
#+end_src

#+RESULTS: t_output_vector
| 1\n2\n |


#+name: t_output_list
#+begin_src perl :results list
print "Test\n";
(1, 2)
#+end_src

#+RESULTS: t_output_list
#+begin_example
- 1
2
#+end_example

#+name: t_output_org
#+begin_src perl :results org
print "Test\n";
(1, 2)
#+end_src

#+RESULTS: t_output_org
#+BEGIN_SRC org
1
2
#+END_SRC

#+name: t_output_html
#+begin_src perl :results html
print "Test\n";
(1, 2)
#+end_src

#+RESULTS: t_output_html
#+BEGIN_HTML
1
2
#+END_HTML

#+name: t_output_latex
#+begin_src perl :results latex
print "Test\n";
(1, 2)
#+end_src

#+RESULTS: t_output_latex
#+BEGIN_LaTeX
1
2
#+END_LaTeX
----------------------------------------------------------------------


--
Daniel M. German                  "I see no good reason why the
                                   views given in this volume
                                   should shock the religious
   Charles Darwin ->               feelings of anyone."
http://turingmachine.org/
http://silvernegative.com/
dmg (at) uvic (dot) ca
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