Place a document at the end but evaluate it at the beginning

Question

I would like to collect certain \newcommands in an appendix, so that each one can have a section explaining itself. However, if I put this appendix at the end of the file, then I can't call the commands in the middle of my text because they won't be defined yet.

Is there any way to force LaTeX to scan a file and execute only the command definitions in it?

Answer 1

Here is a solution that should get you started. Place your \newcommands along with the description in MyPreamble.sty. The format of this file is

\newcommand*{\CommandName}{... command text ...}%
\begin{CommandDescription}
    ... the description of what this macro does goes here ...
\end{CommandDescription}

In the preamble you \include this file via \InputOnlyNewcommands{MyPreamble.sty}, which ignores the description of the macros, and only defines the \newcommands. In the main body you can use these macros as you want. At the end of the document you can have an appendix with these commands and their description via \InputIgnoringNewcommands{MyPreamble.sty}.

In the example below I define three commands along with a description of what they do.

Notes:

• Not sure how to eliminate the quote at the beginning of the command name in the appendix.
• The filecontents package was only used to package this example into a fully compilable example. It is not needed in your real example.
• This only works with \newcommand. That is you can not use \def, \renewcommand, \providecommand, or any of the equivalent macros from the xparse package.

Code:

\documentclass{article}
\usepackage{xcolor}
\usepackage{xparse}
\usepackage{enumerate}
\usepackage{environ}
\usepackage{filecontents}
\begin{filecontents}{MyPreamble.sty}
    \newcommand{\Bold}[2][black]{\textbf{\textcolor{#1}{#2}}}%
    \begin{CommandDescription}
        This macro makes the text parameter bold.
    \end{CommandDescription}
\newcommand*{\BoldBlue}[1]{\Bold[blue]{#1}}%
\begin{CommandDescription}
    This macros makes the text parameter bold, and also in blue.
\end{CommandDescription}

\newcommand*{\BoldRedItalics}[1]{\textit{\Bold[red]{#1}}}%
\begin{CommandDescription}
    This macros makes the text parameter bold, italicized, and also in red.
\end{CommandDescription}

\end{filecontents*}
\NewEnviron{CommandDescription}[1]{}{}%
\newcommand{\InputOnlyNewcommands}[1]{%
    \RenewEnviron{CommandDescription}{}{}%
    \input{#1}%
}%
\newcommand{\InputIgnoringNewcommands}[1]{%
    \RenewEnviron{CommandDescription}{%
        \BODY\par
    }{%
    }%
    \RenewDocumentCommand{\newcommand}{%
        s%    #1 = optional star
        m%    #2 = macro name
        O{0}% #3 = number of parameters (optional, defaults to 1)
        o%    #4 = default value of optional parameter
        m%    #5 = code that was to be executed
    }{%
        \medskip\par\noindent%
        \Bold{\string##2:}
    }%
    \input{#1}%
}%
\InputOnlyNewcommands{MyPreamble.sty}
\begin{document}
\section{Body}
Make \Bold{this bold.}
And in color: \BoldBlue{blue.}
And in color with italics: \BoldRedItalics{red.}
\section{Appendix}
\InputIgnoringNewcommands{MyPreamble.sty}
\end{document}

Answer 2

I think I know what you want. Thanks to @PeterGrill and How display LaTeX code in LaTeX document? this now works:

% preamble.tex
%
% commands here, documented with comments

% \foo does whatever
\newcommand{\foo}{whatever}

Then

\documentclass{article}
\usepackage{verbatim}

\input{preamble} % define your macros

\begin{document}

\section{Contents}
Use macro \foo{}.

\section{Commands I used} % document your macros

   \verbatiminput{preamble}

\end{document}

You won't have LaTeX formatting for your macro documentation. Peter Grill's solution does that.

Edit: This question/answer is related to the naive construction of quines (see Self-replicating (La)TeX document). I use the idiom with \jobname to append TeX source for homework questions to the questions so that students have a template to start with:

% Math 370 hw2
%
\documentclass{article}
\pagestyle{empty}

\usepackage{amsmath}
\usepackage{amsthm}
\usepackage{verbatim}

%% create an environment for theorems
\newtheorem*{thm}{Theorem}

\begin{document}

\begin{thm}
The amount by which the sum of the angles of a spherical triangle
exceeds $\pi$ is proportional to the area of the triangle.
\end{thm}

\verbatiminput{\jobname}

\end{document}