R devel - Sep 2006 - Sweave processes \Sexpr in commented LaTeX source (2.3.1patched and 2.4.0)

Hi all,

On FC5, using:

  Version 2.3.1 Patched (2006-08-06 r38829)

and today's

  R version 2.4.0 alpha (2006-09-19 r39397)

with the following .Rnw file:


\documentclass[10pt]{article}
\begin{document}

   This line should print '2': \Sexpr{1 + 1}
%% This line should NOT print '2': \Sexpr{1 + 1}

\end{document}


The \Sexpr in the second line is processed even though the line is
commented. This results in the following .tex file content (in the case
of R 2.4.0):


\documentclass[10pt]{article}
\usepackage{/home/marcs/R.Files/SourceCode/R-alpha/share/texmf/Sweave}
\begin{document}

   This line should print '2': 2
%% This line should NOT print '2': 2

\end{document}



Shouldn't Sweave just generally ignore commented LaTeX code? In
reviewing Sweave.R I did not see a check for this, so perhaps there are
circumstances where one wants a \Sexpr in commented LaTeX code
processed. An example escapes me at the moment however.

HTH,

Marc Schwartz

>>>>> On Tue, 19 Sep 2006 19:14:39 -0500,
>>>>> Marc Schwartz (MS) wrote:
  > Hi all,
  > On FC5, using:

  >   Version 2.3.1 Patched (2006-08-06 r38829)

  > and today's

  >   R version 2.4.0 alpha (2006-09-19 r39397)

  > with the following .Rnw file:


  > \documentclass[10pt]{article}
  > \begin{document}

  >    This line should print '2': \Sexpr{1 + 1}
  > %% This line should NOT print '2': \Sexpr{1 + 1}

  > \end{document}


  > The \Sexpr in the second line is processed even though the line is
  > commented. This results in the following .tex file content (in the case
  > of R 2.4.0):


  > \documentclass[10pt]{article}
  > \usepackage{/home/marcs/R.Files/SourceCode/R-alpha/share/texmf/Sweave}
  > \begin{document}

  >    This line should print '2': 2
  > %% This line should NOT print '2': 2

  > \end{document}



  > Shouldn't Sweave just generally ignore commented LaTeX code? In
  > reviewing Sweave.R I did not see a check for this, so perhaps there are
  > circumstances where one wants a \Sexpr in commented LaTeX code
  > processed. An example escapes me at the moment however.

Sweave does not parse the LaTeX part of the document at all (which
makes it a lot easier), all it does is looking for its own "magic
strings" and replacing those, wherever they might occur.

If we would start to respect comments, we would need a some kind of
parser for LaTeX, which we currently don't need ... and starting to
parse LaTeX would also open a can of worms of possible requests (what
to do with Sexpr inside verbatim, etc, etc).

Best,
Fritz

Hi.

2006/9/20, Marc Schwartz <MSchwartz a mn.rr.com>:
> Hi all,
>
> On FC5, using:
>
>   Version 2.3.1 Patched (2006-08-06 r38829)
>
> and today's
>
>   R version 2.4.0 alpha (2006-09-19 r39397)
>
> with the following .Rnw file:
>
>
> \documentclass[10pt]{article}
> \begin{document}
>
>    This line should print '2': \Sexpr{1 + 1}
> %% This line should NOT print '2': \Sexpr{1 + 1}
If it's just a comment, why don't use something like:
% \ Sexpr (del the space)
or
%\sexpr (change 'sexpr' with 'Sexpr')
or
%...the 'Sexpr' command (add a backslash in latex code)
?

Antonio.
>
> \end{document}
>
>
> The \Sexpr in the second line is processed even though the line is
> commented. This results in the following .tex file content (in the case
> of R 2.4.0):
>
>
> \documentclass[10pt]{article}
> \usepackage{/home/marcs/R.Files/SourceCode/R-alpha/share/texmf/Sweave}
> \begin{document}
>
>    This line should print '2': 2
> %% This line should NOT print '2': 2
>
> \end{document}
>
>
>
> Shouldn't Sweave just generally ignore commented LaTeX code? In
> reviewing Sweave.R I did not see a check for this, so perhaps there are
> circumstances where one wants a \Sexpr in commented LaTeX code
> processed. An example escapes me at the moment however.
>
> HTH,
>
> Marc Schwartz
>
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