Hi Zdenek,
On 13/04/2020, at 0:00, "Zdenek Wagner"
<[email protected]<mailto:[email protected]>> wrote:
Hi all,
This can be done with \let and \def, not with \newcommand:
\let\savedLabel\label
\def\label#1{Do something with #1 \SavedLabel{#1}}
The second line could be replaced with
\renewcommand*\label[1]{Do something with #1 \SavedLabel{#1}}
This idea can be extended somewhat.
\makeatletter
\def\MY@label#1{Do something with #1 \LTX@label{#1}}
\AtBeginDocument{
\let\LTX@label\label
\let\label\MY@label
}
\makeatother
This way you retain pointers to both your own version and the original,
so can change between them if necessary, within different parts of your
document, or within specially tailored environments.
Delaying the \let rebindings using \AtBeginDocument means that it will still
work
if some other package (such as hyperref ) makes its own changes,
which you also want to incorporate.
\providecommand is useful if you assume that a definition exist but you want to
provide a default definition.
Sure.
It is particularly useful when devising templates that will be filled with
information
provided by a database, and command-line shell software that automates
calls to TeX or LaTeX or other engine.
latex '\def\name{client name} ... \input{mytemplate.tex}'
where mytemplate.tex is the main LaTeX source, having
\providecommand{\name}{some default}
and similarly for all the variable data fields.
I use this kind of setup to automate personalised assignment cover-sheets,
generated online in response to student requests from a web page.
Sometimes the full question sheet is done this way,
with versions personalized, or randomized, based upon student ID numbers.
The newcommand family is useful because it offers a default first argument but
if you use arguments with the newcommand family, use always the star version so
that the macro is not \long. If you forget a right brace after an argument, you
will get an error message at the end of a paragraph but without the star you
get an error message at the end of a file hence it is difficult the source of
the error.
Construct \csname scenename\endcsname expands to the contents of \scenename if
already defined or is defined to be identical with \relax if not yet defined.
When checking existence of definition, LaTeX does the following:
\expandafter\ifx\csname scenename\endcsname\relax
code for \scenename not yet defined
\else
code for \scenename already defined
\fi
With \csname you can test for all kinds of things,
and even adjust macros like \begin and \end to patch in extra coding
for specific environments, whether a package is loaded or not.
The possibilities are endless.
Cheers.
Stay safe.
Ross
Of course, the whole \else part can be omitted if you have nothing to put there.
Zdeněk Wagner
http://ttsm.icpf.cas.cz/team/wagner.shtml<https://protect-au.mimecast.com/s/QcrSCnx1Z5UgvO8wS9Msu9?domain=ttsm.icpf.cas.cz>
http://icebearsoft.euweb.cz<https://protect-au.mimecast.com/s/fkdBCoV1Y2S5EqO9HzWPDx?domain=icebearsoft.euweb.cz>
ne 12. 4. 2020 v 12:49 odesílatel Ross Moore
<[email protected]<mailto:[email protected]>> napsal:
Hi Phil, Zdeněk and others.
On 12 Apr 2020, at 7:46 pm, Philip Taylor
<[email protected]<mailto:[email protected]>> wrote:
Zdeněk Wagner wrote:
I would not do it. Of course, you cannot use \renewcommand because
\scenename is not used in any *.ldf. You could use \def\scenename{दरश्य} […]
LaTeX has \providecommand with the same syntax as \newcommand and
\renewcommand .
It makes the definition *only* if the c-s is not already known.
This means that you can always use:
\providecommand\mycs{}
\renewcommand\mycs{ what I really want }
to get around such issues.
A thought — if \scenename is not known at the point that the last line of
[gloss-]marathi.ldf is read, would there be any point in using \def \scenename
{दरश्य}, since such definition would either get over-ridden by whatever
subsequent definition of \scename is causing the problem (\def, \renewcommand),
or would prevent a subsequent \newcommand from working as \scenename would
already be defined. Is this not the case (he asked, as someone who barely
understands anything that LaTeX does ...) ?
There is always a way to get what you want,
whether using Plain TeX or LaTeX or whatever other high-level macro structures.
Thus the important thing is how to make it resistant to updates, as Zdeněk said.
Philip Taylor
Hope this helps.
Stay safe.
Ross
Dr Ross Moore
Department of Mathematics and Statistics
12 Wally’s Walk, Level 7, Room 734
Macquarie University, NSW 2109, Australia
T: +61 2 9850 8955 | F: +61 2 9850 8114
M:+61 407 288 255 | E: [email protected]<mailto:[email protected]>
http://www.maths.mq.edu.au
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