Ceci est une ancienne révision du document !
—
ID: Q-whatenv
section: Bits and pieces of (La)TeX
revised: 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 %} –>
