Does \newenvironment have a \provideenvironment cousin, as \newcommand has \providecommand?

Question

To avoid the problem of having to decide whether to use \newcommand or \renewcommand, LaTeX has the option of \providecommand.

Is there something corresponding to this for environments? I'd like to be able to type \provideenvironment (or similar) rather than first using \newenvironment and then using \renewenvironment.

Good question! I think that anyone writing a generic newX macro ought to also provide both renewX and provideX variants. (I got so fed up of journals defining all different types of theorem variants - and therefore messing up my own definitions - that I wrote a \providetheorem command.) — Andrew Stacey, Jun 14 '11 at 10:07
It's worth pointing out that \providecommand isn't to avoid having to decide which to use, it's to provide a definition if one does not already exist. If it does, then \providecommand does not redefine it. — TH., Jun 14 '11 at 10:37
Yes, I think that's probably a better description of its intended usage. But because I often generate LaTeX automatically it's quite convenient for me to use \providecommand rather than keep track of whether my LaTeX code has already defined a command (hence the weird way I described its purpose). — bryn, Jun 19 '11 at 07:49

score 27 · Accepted Answer · answered Jun 14 '11 at 10:03

I don't believe there is a \provideenvironment defined anywhere, but you can define it.

\documentclass{article}

\makeatletter
\def\provideenvironment{\@star@or@long\provide@environment}
\def\provide@environment#1{%
        \@ifundefined{#1}%
                {\def\reserved@a{\newenvironment{#1}}}%
                {\def\reserved@a{\renewenvironment{dummy@environ}}}%
        \reserved@a
}
\def\dummy@environ{}
\makeatother

\provideenvironment{foo}[1][blarg]{begin foo: #1 }{end foo}
\provideenvironment{foo}{asdf}{asdf}
\begin{document}
\begin{foo}
whee
\end{foo}
\end{document}

The first time foo gets defined. The second time it does not because it is already defined.

Like! Can you tell us/point us to what \@star@or@long is and does? It appears very mystical ... — Bananguin, Oct 29 '13 at 12:00
@user1129682: \@star@or@long is defined in the latex kernel (ltdefns.dtx): "Look ahead for a *. If present reset l@ngrel@x so that the next definition, #1, will be non-long". — wasteofspace, Nov 20 '13 at 13:12

Leo Liu · Answer 2 · 2011-06-14T10:18:26.913

13

No.

If you are familiar with expl3 (but not necessary), you can use \ProvideDocumentEnvironment in xparse package. The syntax is a little different. For example:

\usepackage{xparse}
\ProvideDocumentEnvironment{foo}{ o m }{%
  \IfNoValueTF{#1}{only #2}{#1 and #2}%
}{%
  \IfNoValueTF{#1}{only #2}{#1 and #2}%
}

edited Jun 14 '11 at 10:18

answered Jun 14 '11 at 10:06

Leo Liu

77,365

score 5 · Answer 3 · edited Nov 20 '13 at 13:02

5

There is a \provideenvironment in the package makecmds. I suppose that is what you are looking for. Its syntax is analog to that of \newenvironment.

edited Nov 20 '13 at 13:02

lockstep

250,273

answered Nov 20 '13 at 12:59

Supernormal

842
8
12

Does \newenvironment have a \provideenvironment cousin, as \newcommand has \providecommand?

3 Answers3

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