[l2h] Re: renewcommand including \section gets lost

[Ross Moore]

Hi Julius,

It is very dangerous to use section-commands, such as
   \section , \subsection, \paragraph  etc.
within the expansion of macros redefined using \renewcommand .

The reason that the behaviour with \newcommand and \renewcommand
is different is that every instance a command defined via \newcommand  is
replaced very early in the processing, *before* the document is broken
into segments.
On the other hand, when  \renewcommand  is used, the macro is not
replaced early but instead "wrapped" to cause it to be replaced
in sequence with environments and other "context-sensitive" macros.

The difference is that if a command has been \renew'd once, then it
may well be renew'd more than once; so it cannot be assumed to have a
constant replacement throughout the whole document.
(Note that the expansion model for LaTeX2HTML differs from that
for TeX engines generally.)


How does this affect sectioning commands ?
Well, the document gets broken-up into pieces corresponding
to the recognisable sections. Then each of these sections
is processed (more or less independently) to make the individual HTML
pages. For this to work with your \ksectionalt command, you need
the replacements to have been made *before* the document is split
into pieces -- this precludes the use of \renewcommand, as explained
above.

The correct coding for what you are trying to achieve is:


\usepackage{html}  %  always load this with LaTeX2HTML documents


%begin{latexonly}
\newcommand{\ksectionalt}[4]{\section[#4]{#3}\chlabel{#1}\index{#2|textbf}}
%end{latexonly}
\begin{htmlonly}
 \newcommand{\ksectionalt}[4]{\section{#3}}
\end{htmlonly}



On Thu, 9 Oct 2003, Julius Smith wrote:

> Oops - my "work around" does not really work around the problem.  The
> second newcommand is simply ignored. -- jos
>
> At 12:58 AM 10/9/2003 -0700, Julius Smith wrote:
> >Here's an odd one:
> >
> >I have a macro I normally use for section headings defined as follows:
> >
> >\newcommand{\ksectionalt}[4]{\section[#4]{#3}\chlabel{#1}\index{#2|textbf}}
> >
> >In a particular document, I tried to override this with a simpler version
> >as follows:
> >
> >...
> >\renewcommand{\ksectionalt}[4]{\section{#3}}

No -- don't do this!
Your document only uses one expansion for  \ksectionalt
so just set it once --- using "conditional" environments
to get different expansions with different processing engines.


> >\begin{document}
> >...
> >
> >It works for LaTeX, but not for l2h.  While I see a message that

Correct. To guarantee well-formed (and usually valid) HTML, the way
macro definitions are handled by laTeX2HTML has significant differences
from what (La)TeX does.

> >ksectionalt has been redefined, it is not found at the end during section
> >linking.  I see the following in the WARNINGS file:
> >
> >Doing section links ......
> >...
> >*** wrap_cmd_ksectionalt not defined, cannot wrap \ksectionalt

This at least tells you that something isn't right.

Wrapping would not work anyway, since after "splitting" you
would get part of the wrapper in one segment, with the rest
of it in the next segment.

> >
> >
> >Changing "renewcommand" to "newcommand" in an htmlonly block works around

Yes; for the reasons described above.

> >the problem. ("providecommand" acts like renewcommand.)

\providecommand  should do nothing if \newcommand has occurred already.

> >
> >Julius

Hope this helps,

	Ross Moore


>
> _____________________________
> Julius O. Smith III <jos at ccrma.stanford.edu>
> Assoc. Prof. of Music and (by courtesy) Electrical Engineering
> CCRMA, Stanford University
> http://www-ccrma.stanford.edu/~jos/
>
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