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— section: Bits and pieces of (La)TeX date: 2014-06-10 — # What are LaTeX environments

While TeX makes direct provision for commands, LaTeX adds a concept of environment; environments perform an action on a block (of something or other) rather than than just doing something at one place in your document.

A totally trivial environment could change the font in use for a chunk of text, as ```latex \newenvironment{monoblock}%

{\ttfamily}%
{}

``` which defines a `monoblock` which may be used as ```latex \begin{monoblock}

some text set in monospace

\end{monoblock} ``` which will look like:

`some text set in monospace`

so it is a particularly simple example. A rather complicated environment is introduced by `\begin{document}`; it looks simple, but needs all sorts of special TeX code to make it work transparently; most environments are more elaborate than `monoblock` and _much_ simpler than `document`.

An environment puts its content inside a TeX _group_, so that commands used inside the environment don't leak out — the `monoblock` environment, above, restricts its effect to its own contents (the stuff between the `\begin{monoblock}` and `\end{monoblock}`), which is just what you need for this sort of thing.

So that's simple environments; the `monoblock`, above doesn't actually gain us much over ```latex {\ttfamily some text set in monospace} ``` though in fact many useful environments are just as simple (to look at). Some, such as `verbatim`, look simple but are actually very tricky inside.

LaTeX also allows arguments to an environment: ```latex \newenvironment{fontblock}[1]%

{#1\selectfont}%
{}

``` and use of `fontblock` as: ```latex \begin{fontblock}{\ttfamily} ``` would produce the same effect as the `monoblock` environment.

Environments may also have optional arguments, in much the same way as commands: ```latex \newenvironment{normaltext}[1][\itshape]%

{#1}%
{}

``` which will ordinarily set its body in italic, but ```latex \begin{normaltext}[\ttfamily]

...

\end{normaltext} ``` will observe its optional argument, and behave the same as the `monoblock` we started with.

Note that an environments argument(s) (mandatory or optional) are _not_ passed to the `\end` text of the environment — that is specified as a macro with no arguments, so that ```latex \newenvironment{normaltext}[1][\itshape]%

{#1}%
{\typeout{what was #1, again?}

``` produces an error message ```latex ! Illegal parameter number in definition of \endnormaltext. ``` So, if you need to pass an environment argument to the end-code, you have to wrap it in a macro of its own: <!– {% raw %} –> ```latex \newenvironment{normaltext}[1][Intro]%

{#1%
 \newcommand{\foo}{#1}}%
{\typeout{what was \foo{}, again?}

``` <!– {% endraw %} –>

2_programmation/macros/que_sont_les_environnements.1527110887.txt.gz · Dernière modification: 2018/05/23 23:28 par joseph.wright
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