Testing if \BODY is empty in Environ

Question

I would like to test whether the string in \expandafter\long\expandafter\xdef\csname\currfilebase\Introduction is empty so that the section is not displayed. This environment introduction is defined in a file in P/Fourier.tex. Of course, what I did here does not work. I have tried many if the \if... commands from etoolbox but all seem to not work. (tried here).

\documentclass[11pt]{scrreprt}

\usepackage{currfile}
\usepackage{filehook}
\usepackage{environ}

\usepackage{etoolbox}


\def\Introduction{Introduction}


\NewEnviron{introduction}{%
      \expandafter\long\expandafter\xdef\csname\currfilebase\Introduction \endcsname{\expandafter\unexpanded\expandafter{\BODY}}%
}%


\AtEndOfIncludes{%
  \ifcurrfiledir{P/}{%
    \ifdefequal{\csname\currfilebase\Introduction\endcsname}{ }{True}{False}%
    \section{Introduction}%
    \csname \currfilebase \Introduction \endcsname}%
}%

\begin{document}    
\include{P/Fourier}
\end{document}

And P/Fourier.tex contains

\begin{introduction}
Test
\end{introduction}

I have a couple of those environment and I wish that they are not shown in the final pdf. So I have something like this if the file is empty:

Edit: Fixed the missing } and removed an irrelevant line.

Edit #2: I have changed this to the following code (with etoolbox):

\ifcsvoid{\currfilebase\Introduction}{}{%
      \section{Introduction}%
      \csname\currfilebase\Introduction\endcsname}%

This seems to work! Is this a good way of doing things? Thanks guys, now I have also learned \show which helped a lot!

Edit #3: Since I am already using etoolbox I can do use all others commands as well anyway, so

\newcommand{\makesection}[1]{\ifcsvoid{\currfilebase#1}{}%
  {%
    \section{#1}%
    \csuse{\currfilebase#1}%
  }%
}%

(I have done the same in the rest too)

Answer 1

That is already quite nice, what you did there, Jonas, and would probably have justified a self-answer. I only added some small changes:

\documentclass[11pt]{scrreprt}

\usepackage{currfile}
\usepackage{filehook}
\usepackage{environ}

\usepackage{etoolbox}

\def\introductionname{Introduction}
\def\methodsname{Methods}
\def\ideasname{Ideas}

\newcommand\defenviron[1]{\NewEnviron{#1}{\expandafter\long\expandafter\xdef\csname\currfilebase #1\endcsname{\expandafter\unexpanded\expandafter{\BODY}}}}

\defenviron{introduction}
\defenviron{methods}
\defenviron{ideas}

\newcommand\makesection[1]{\ifcsvoid{\currfilebase #1}{}%
  {%
    \section{\csname#1name\endcsname}%
    \csuse{\currfilebase #1}%
  }%
}%

\AtEndOfIncludes{%
    \ifcurrfiledir{P/}{%
        \makesection{introduction}%
        \makesection{methods}%
        \makesection{ideas}%
        }{}%
}%

\begin{document}    
    \include{P/Fourier}
\end{document}

First of all I put those environment definitions in their own command \defenviron for convenience. Second I changed the naming scheme just a litte. Then I also added the missing false case for \ifcurrfiledir. But that's about it.

You could probably also loop over the environments in those two places, if the code is really this uniform.

Answer 2

You have a missing } in your code, if I fix that and then arrange the thing so it works in my directory setup and add

\expandafter\show\csname\currfilebase\Introduction\endcsname

Just before your test then I get

\env2-aIntroduction=\relax.

If there is no introduction at all and

> \env2-aIntroduction=\long macro:
->\ignorespaces .

If there is an empty introduction.

So you need to test if it has a definition just consisting of \ignorespaces (or don't add \ignorespaces unconditionally in your definition.

I then stopped at

! Undefined control sequence.
\scr@ds@tocentry ->\convertchar 

which is I assume an unrelated local macro? so am not including a working version of the document as I would normally do.