Cfrgtkky

I'm trying to create an environment which uses xparse style arguments but I have to be able to use the whole environment content in the environment definition, e.g. as an argument.

Ideally I'd like to write something like

DeclareCollectedDocumentEnvironment { env } { o } {

    Make use of optional Argument #1 and Content CollectedBody.

}

begin{env}[optional]

    content

end{env}

Is there a reason, why xparse doesn't provide something like this?

Using NewEnviron from the environ package does not work for me, because I'm reliant on some of the argument-parsing features xparse provides.

Currently I've got this working:

documentclass{article}

usepackage{xparse}

usepackage{environ}



ExplSyntaxOn



DeclareDocumentCommand { myenv } { o uq_nil } {

    opt:~#1 \

    content:~#2

}

cs_set:Npn myenv_collect:n #1 {

    myenv #1 q_nil

}

makeatletter

DeclareDocumentEnvironment { env } { } {

    Collect@Body myenv_collect:n

} { }

makeatother



ExplSyntaxOff



begin{document}



begin{env}[99]

    With optional argument

end{env}



begin{env}

    Without optional argument

end{env}



end{document}

This however has some flaws:

• Multiple paragraphs inside the environment cause an infinite loop


• Nesting does not work as expected

I've also tried to declare the arguments for DeclareDocumentEnvironment and somehow pass them onto myenv_collect:n, but the behaviour of Collect@Body made it difficult.

Is there a solution to my problem, preferably a latex3 one?

An interface similar to NewEnviron would be a welcome addition to xparse; but you can use it indirectly:

documentclass{article}

usepackage{xparse,environ}



NewDocumentEnvironment{env}{ O{default} }

 {Environenv{#1}}

 {endEnvironenv}



NewEnviron{Environenv}[1]

 {Do something with #1 and BODY}



begin{document}



begin{env}

What is this?



Another paragraph.

end{env}



begin{env}[foo]

What is this?



Another paragraph.

end{env}



end{document}

If you call the command form of Environenv, it will know what environment it's been called in. That's the same trick for defining environments containing align in amsmath.

Important news (March 2019)

With the release 2019-03-05 release of xparse, the functionality of environ has been implemented, with some adaptations. See below for a description.

^{Due to freezing of TeX Live, it is currently only available in TL2019/pretest or MiKTeX.}

The above code can be reduced to

documentclass{article}

usepackage{xparse}



NewDocumentEnvironment{env}{O{default}+b}

 {Do something with #1 and #2}

 {}



begin{document}



begin{env}

What is this?



Another paragraph.

end{env}



begin{env}[foo]

What is this?



Another paragraph.

end{env}



end{document}

Some notes: the argument specifier b denotes the body of the environment, which will be then collected as a macro argument, just like environ did. There is no BODY to use: in this case b is the second argument, so one refers to it as #2.

The “end part” is to be specified, although it will be usually empty.

If paragraphs are expected in the body, the argument should be specified as +b, like all other “long arguments”.