How to create fancy table of equations (to be typeset before the equations are rendered in text)

Question

Is there a way to create a command which adds to a table or otherwise typesets in a place specified by the user? Example of what I'm after

\documentclass{article}
\begin{document}
\tableofequations

\begin{equation}
e^{i\pi} = -1
\end{equation}\rememberequation{e^{i\pi}=-1}{Euler's Equation}

\end{document}

Where the \tableofequations command would render something like

%with \usepackage{array}
\begin{center}
\begin{tabular}{m{0.3\linewidth} m{0.3\linewidth} m{0.3\linewidth}}
Equation & Name & Page \\\hline
\[e^{i\pi} = -1\] & Euler's Equation & Page 1\\\hline
\end{tabular}
\end{center}

The effect I'm after is almost exactly recorded in this answer with the only difference being the facility to place the equation table before the equation is rendered (as a table of figures renders the captions before the figures are typeset). Possibly to be achevied through an auxilliary file, although I have almost no knowledge of how these work.

Answer 1

This code uses the .aux file to store the relevant information. \rememberequation both typesets and saves the equation. On the second run, the data is automatically read in at the beginning of the document, building (a long) macro \listofequations, which is then used by \tableofequations to typeset the table (anywhere in the document).

\documentclass{article}
\usepackage{etoolbox}

\makeatletter
\newcommand\rememberequation[2]{%
  \begin{equation}#1\end{equation}%
  \protected@write\@mainaux{}
    {\detokenize{\gappto\listofequations}{%
        (\theequation)&
        \detokenize{$#1$}&
        \detokenize{#2}&
        \thepage\\
      }%
    }%
}
\makeatother
\newcommand\tableofequations{%
  \preto\listofequations{%
    \begin{tabular}{cccc}
      \#&Equation&Name&Page\\\hline
  }%
  \appto\listofequations{%
    \hline
    \end{tabular}
  }%
  \begin{center}
    \listofequations
  \end{center}
}

\begin{document}
\tableofequations

\rememberequation{e^{i\pi}=-1}{Euler's Equation}
\rememberequation{e^{i\pi}=-1}{Euler's Equation, again}
\newpage
\rememberequation{e^{i\pi}=-1}{Euler's Equation, yet again}

\end{document}

EDIT: the fancy version requested in the comment

So, the idea is that we write equations in the usual equation environment and trigger the "remembering" code by \caption. (I believe \caption is a better choice than \label.)

Before the code, a disclaimer. This is a hack. I have no idea what trouble it might cause in conjunction with some package ...

\documentclass{article}
\usepackage{etoolbox}
\usepackage{environ}

\makeatletter

\AtBeginEnvironment{equation}{%
  \Collect@Body\rememberequation
}

\newtoks\currentequation
\def\rememberequation#1{%
  \typeout{DEBUG: \detokenize{#1}}%
  % #1 starts with \csname equation\endcsname
  \expandafter\currentequation\expandafter{#1}%
  \let\caption\storecurrentequation
  #1%
}

\def\storecurrentequation#1{%
  \protected@write\@mainaux{}%
    {\detokenize{\gappto\listofequations}{%
        (\theequation)&
        $\expandafter\detokenize\expandafter{\the\currentequation}$&
        \detokenize{#1}&% #1 = caption
        \thepage\\
      }%
    }%
}

\newcommand\tableofequations{%
  \preto\listofequations{%
    \begin{tabular}{cccc}
      \#&Equation&Name&Page\\\hline
  }%
  \appto\listofequations{%
    \hline
    \end{tabular}
  }%      
  \begin{center}
    \let\equation\relax
    \let\label\@gobble
    \let\caption\@gobble
    \listofequations
  \end{center}
}

\makeatother


\begin{document}
\tableofequations

\def\caption#1{}

\begin{equation}
  \label{eq:1}
  e^{i\pi}=-1
  \caption{Euler's Equation}
\end{equation}

\begin{equation}
  \label{eq:2}
  e^{i\pi}=-1
  \caption{Euler's Equation, again}
\end{equation}

\newpage
\begin{equation}
  \label{eq:3}
  e^{i\pi}=-1
  \caption{Euler's Equation, yet again}
\end{equation}

\end{document}