Comment mettre des caractères autres que des lettres dans les noms de commande ? [FAQ LaTeX]

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====== Comment mettre des caractères autres que des lettres dans les noms de commande ? ======

Les utilisateurs débutants avec <latex>\LaTeX</latex> sont souvent étonnés de voir que des commandes contenant des caractères autres que des lettres ne fonctionnent pas. Par exemple :
<code latex>
\newcommand{\a2main}{À demain !}
</code>

En effet, contrairement à d'autres langages de programmation, <latex>\TeX</latex> n'autorise que [[2_programmation:macros:que_sont_les_macros|des lettres dans les noms de commandes]]. Il existe cependant des techniques pour contourner cette limitation mais elles ne sont pas sans défaut.

===== Utilisation de “\csname” et “\endcsname” =====

Voici un exemple de la méthode utilisant les commandes ''\csname'' et ''\endcsname''.

<code>
\expandafter\newcommand\csname a2main\endcsname{À demain !}
Je vous dis « \csname a2main\endcsname ».
</code>

Cette technique a l'unique désavantage de demander d'être bien trop verbeuse.

FIXME //Traduction à poursuivre.//

2. Define a "special-command generator", and  use the resulting commands:

<code latex>
\newcommand{\DefineRemark}[2]{%
  \expandafter\newcommand\csname rmk-#1\endcsname{#2}%
}
\newcommand{\Remark}[1]{\csname rmk-#1\endcsname}
 ...
\DefineRemark{cul8r}{Goodbye!}
 ...
\Remark{cul8r}
</code>

  * **Pro:** Straightforward to use, not too untidy
  * **Con:** It's hardly doing what we set out to do (experts will see that you are defining a macro, but others likely won't)


3. Convince TeX that ''8'' is a letter:

<code latex>
\catcode`8 = 11 
\newcommand{\cul8r}{Goodbye!}
I said, ``\cul8r''.
</code>

  * **Pro:** ''\cul8r'' can be used directly
  * **Con:** Likely to break other uses of ''8'' (such as numbers or dimensions; so ''\setlength{''\paperwidth''}{8in}'' tells us:

<code>
! Missing number, treated as zero.
<to be read again> 
                   8
</code>


As a general rule, changing category codes is something to use
//in extremis//, after detailed examination of options.  It is
conceivable that such drastic action could be useful for you, but
most ordinary users are well advised not even to try such a technique.

4.  Define a macro ''\cul'' which must always be followed by ''8r'':

<code>
\def\cul8r{Goodbye!}
I said, ``\cul8r''.
</code>

  * **Pro:** ''\cul8r'' can be used directly
  * **Con #1:** Breaks if ''\cul'' is followed by anything other than ''8r'', with a confusing diagnostic, as ''\cul99'' produces:

<code>
! Use of \cul doesn't match its definition.
<*> \cul9
         9
</code>
(which would confuse someone who hadn't even realised there //was// a definition of ''\cul'' in the document).

  * **Con #2:** Silently redefines existing ''\cul'', if any; as a result, the technique cannot be used to define both a ''\cul8r'' and, say, a ''\cul123'' macro in the same document.


Technique 3 is in fact commonly used --- in a limited form --- within
most LaTeX packages and within LaTeX itself.  The convention is to
use ''@'' within the names of internal macros to hide them
from the user and thereby prevent naming conflicts.  To this end,
LaTeX automatically treats ''@'' as a letter while
processing classes and packages and as a non-letter while processing
the user's document.  The key to this technique is the separation:
internally a non-letter is used for macro names, and the user doesn't
see anything of it, while the status remains "frozen" in all the
definitions created within the class or package.  See 
[[FAQ-atsigns|\@ and @ in macro names]] for
more information.

Note that analogous use of technique 3 in this example would give us

<code latex>
\begingroup
  \catcode`8 = 11 
  \gdef\cul8r{Goodbye!}
  \gdef\later{\cul8r}
\endgroup
I said, ``\later''.
</code>
which works, but rather defeats the object of the exercise.
(''\later'' has the "frozen" catcode for "8", even though the value
has reverted to normal by the time it's used; note, also, the use of
the primitive command ''\gdef'', since ''\newcommand'' can't make a
macro that's available outside the group.)

//Recommendation//: Either choose another mechanism (such as
''\DefineRemark'' above), or choose another name for your macro, one
that contains only ordinary letters.  A common approach is to use
roman numerals in place of arabic ones:

<code latex>
\newcommand{\culVIIIr}{Goodbye!}
</code>
which rather spoils the intent of the joke implicit in the example ''\cul8r''!

-----
//Source:// [[faquk>FAQ-linmacnames|Non-letters in macro names]]

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