Automate the description of the paper

Question

Most or all papers have a final paragraph in the introduction that describes the sections that are present. I'd like to generate it automatically, I guess this should be possible because it is mostly like an index, but in fact I have no idea about how this could be done (therefore I can't provide a mwe, I'm very sorry for this).

My guess is that it should be possible to add a description for each section, something like:

\section{Preliminaries}
\label{sec:preliminaries}
\description{we introduce the concepts that will be relevant along the paper}

What I would like is to insert at the end of the introduction something like this:

\descriptions{}

Which should expand to:

The structure of the paper is as follows: In Section 2 we introduce the concepts that will be relevant along the paper. In Section 3 we...

This is pretty much like the table of contents (TOC) that you would find in any book, this is prose and not a table and there is one additional field, but in short it's the same. Seems feasible.

Pointers to what should I check are also welcome, I really have no idea. I don't know how those TOCs are generated either.

PD: I'd prefer not to destroy the possibility of having a regular TOC additionally to this, i.e. I'd prefer not to modify the commands for the TOC (but maybe duplicate some of them).

PD: I found this package, but I get an error (\l@paragraph undefined) http://texblog.org/2008/07/13/define-your-own-list-of/

Answer 1

Use the already provided infrastructure; we use a supplementary “table of contents”, which doesn't interfere with the standard one.

Just initialize the production of this “table of contents” and add a command \l@desc that will be used for printing the entries gathered in the previous run. Of course, two runs are necessary for synchronizing.

\documentclass{article}

\makeatletter
\newcommand{\sectiondescriptions}{%
  \par
  The structure of the paper is as follows.
  \par
  \@starttoc{dsc}%
}
\newcommand{\sectiondescription}[1]{%
  \addcontentsline{dsc}{desc}{In Section \thesection\space#1}%
}
\newcommand{\l@desc}[2]{#1\par}
\makeatother

\begin{document}

\section{Introduction}

We say something about the paper.

\sectiondescriptions

\section{Preliminaries}\label{sec:preliminaries}
\sectiondescription{we introduce the concepts that will be relevant along the
  paper.}

\section{Conclusion}
\label{sec:conclusion}
\sectiondescription{we are done.}

\end{document}

Answer 2

Compiling this twice does what you ask for. It's a little fragile.

Edited to use @Dan 's \InputIfFileExists but still prefer closing the file explicitly.

\documentclass{article}

\newcommand{\structure}{\InputIfFileExists{structure}{}}

\newcommand{\beginstructure}[1]{%
\newwrite\delayedtext
\immediate\openout\delayedtext=structure.tex
\immediate\write\delayedtext{#1}
}

\newcommand{\addtostructure}[1]{%
\immediate\write\delayedtext{%
In Section \arabic{section} #1}
In this section #1 
}

\newcommand{\myendstructure}{% 
\immediate\closeout\delayedtext
}

\begin{document}
\structure

\beginstructure{The structure of the paper is as follows.}

\section{Preliminaries}
\label{sec:preliminaries}
\addtostructure{we introduce the concepts that will be relevant along the
  paper.}

\section{Conclusion}
\label{sec:conclusion}
\addtostructure{we are done.}

\myendstructure
\end{document}

Edit: If you don't like the tex extension on the auxiliary file you can give it any extension you like, and name it with the tex source filename - for example

\immediate\openout\delayedtext=\jobname.struct
...
\newcommand{\structure}{\InputIfFileExists{\jobname.struct}{}}