Dependencies between sections

Question

I'm writing a document such as the following one:

\section{A}\input{A}
\section{B}\input{B}
\section{C}\input{C}
...

Each section provides some content but requires other sections to be included before. For example, B could require A and C, C could require A, and A could require nothing. In this case, the above piece of code should just put A and C in the output document as B is before C. I tried something with the ifthen package, but I failed to obtain a solution that doesn't produce a compilation error if the order is wrong. In particular, it complains about undeclared boolean variables, as it may happen I check for a boolean variable before the section that declares it is loaded.

Any idea? Thank you.

Answer 1

Based on Caramdir's comment, this is how I will do this in ConTeXt. Perhaps someone can translate the solution to LaTeX

\unprotect
\def\markedinput#1%
  {\letvalue{@@input@@#1@@}\empty
    \inputgivenfile{#1}}

\def\checkdependency#1%
  {\doifundefined{@@input@@#1@@}\endinput}

\protect

Then use

\section{A}\markedinput{A}
\section{B}\markedinput{B}
\section{C}\markedinput{C}

and each file can start with

\checkdependency{A}
\checkdependency{C}

Of course, this cannot check future dependencies.

Answer 2

Would something like the following work?

\let\sectionAincluded\relax
This is section A.

\ifx\sectionAincluded\relax
  \ifx\sectionCincluded\relax
    \let\sectionBincluded\relax
    This is section B.
  \fi
\fi

\ifx\sectionAincluded\relax
  \let\sectionCincluded\relax
  This is section C.
\fi

Here \ifx tests whether \sectionXincluded is defined and equivalent to \relax (instead of \relax on could use any other token).

EDIT: turning Aditya's answer into something non-ConTeXt-dependent:

%in main.tex
\makeatother
\def\markedinput#1%
  {\expandafter\let\csname @@input@@#1@@\endcsname\empty
    \input{#1}}

\def\checkdependency#1%
  {\expandafter\ifx\csname @@input@@#1@@\endcsname\empty\else\endinput\fi}
\makeatletter

% A.tex
This is section A.

% B.tex
\checkdependency{A}
\checkdependency{C}
This is section B.

% C.tex
\checkdependency{A}
This is section C.

Answer 3

I think what you're after here is a topological sorting of your sections. This is actually fairly easy to do. Here's a fully LaTeX solution (no plain TeX macros used at all).

\begin{filecontents}{A.tex}
\depend{B}
\depend{C}
\section{A}
This depends on B and C.
\end{filecontents}
\begin{filecontents}{B.tex}
\depend{C}
\section{B}
This depends on C.
\end{filecontents}
\begin{filecontents}{C.tex}
%\depend{B}
\section{C}
Uncommenting the \verb+\depend{B}+ causes a circular dependency.
\end{filecontents}

\documentclass{article}
\usepackage{etoolbox}
\usepackage{currfile}
\newcommand*\depend[1]{%
    \ifcsdef{depend@#1}{}{%
        \ifcsdef{resolving@#1}{%
            \circulardependencyerror
        }{}%
        \cslet{resolving@\currfilebase}\relax
        \input{#1}%
        \csundef{resolving@\currfilebase}%
        \cslet{depend@#1}\relax
    }%
}
\begin{document}
\depend{A}
\end{document}

The filecontents environment just causes TeX to write these files out verbatim.

\depend checks if its argument has already been input. If it has, nothing happens. If it has not, it checks to see if it was in the process of being \input. If so, then there's a circular dependency that needs to be resolved. If it isn't circular, then it inputs the file and marks it as complete.