%
% Copyright (C) 2019 Javier Bezos http://www.texnia.com
%
% This file may be distributed and/or modified under the conditions of
% the MIT License. A version can be found at the end of this file.
%
% Repository: https://github.com/jbezos/gindex
%

\documentclass[a4paper]{ltxguide}

\title{\textsf{gindex}\\\large Version 0.2}

\author{Javier Bezos\\\texttt{http://www.texnia.com}}

\date{2019-10-07}

\raggedright
\parskip=.8ex
\advance\oddsidemargin-.7cm
\advance\textwidth2cm
\addtolength{\textheight}{3.5cm}
\addtolength{\topmargin}{-2cm}

\usepackage{xcolor,bera}

\definecolor{notes}{rgb}{.75, .3, .3}%

\makeatletter
\def\@begintheorem#1#2{%
  \list{}{}%
  \global\advance\@listdepth\m@ne
  \item[{\sffamily\bfseries\color{notes}\MakeUppercase{#1}}]}%
\makeatother
\newtheorem{warning}{Warning}
\newtheorem{note}{Note}
\newtheorem{example}{Example}

\begin{document}

\vspace*{1cm}
{\fontsize{48}{48}\selectfont \color{notes}{gindex}\par}
{\LARGE Formatting indexes with \LaTeX\par}
\vspace*{1ex}
Version 0.2 (2019-10-07)\par
\texttt{https://github.com/jbezos/gindex}\par
Javier Bezos (\texttt{http://www.texnia.com})\par

\vspace*{6ex}

This package works in conjunction with a \textit{\bfseries g}eneric
\verb|ist| file, which provides a way to \textit{\bfseries g}enerate
the format of index entries from within \LaTeX. With standard classes,
it works out of the box with some predefined values, which you can (and
in fact should) redefine with |\renewcommand|.

Note it is version 0.2. Changes of the existing features are unlikely
to happen (but who knows), but new features, on the other hand, will be
added in the near future.

What it does is to generate blocks like this for each first-level entry:
\begin{verbatim}
  \setcounter{indexsubitems}{2}%     The number of subitems
  \indexitem{blah1}{1}%
    \indexsubitem{subblah1}{3}%
    \indexsubitem{subblah2}{5}%
  \indexnoitem{}{}%                  Usually dummy
\end{verbatim}

As you can see, when |\indexitem| is executed, you know the number of
subitems, which is necessary for some styles. Subsubitems are allowed,
but not counted. Only subitems are counted.

The default values are:
\begin{verbatim}
\newcommand\indexitem[2]{\item #1\ifx\\#2\\\else, #2\fi}
\newcommand\indexsubitem[2]{\subitem #1\ifx\\#2\\\else, #2\fi}
\newcommand\indexsubsubitem[2]{\subsubitem #1\ifx\\#2\\\else, #2\fi}
\end{verbatim}
For example, to replace the comma by a quad:
\begin{verbatim}
\renewcommand\indexitem[2]{\item #1\ifx\\#2\\\else\quad #2\fi}
\end{verbatim}

It is guaranteed that these command can take up to 5 arguments. If you
define |\indexitem| with all of them, the parameters in the previous
example will be:
\begin{enumerate}
  \item |blah1|
  \item |1|
  \item |\indexsubitem|
  \item |subblah1|
  \item |3|
\end{enumerate}
This explains the line |\indexnoitem{}{}| above, which by default does
nothing. By inspecting the third parameter you decide how to format the
current parameter (of course, in most cases you must emit it again at
the end of your definition of |\indexitem|). See the example below.

There is a tool to define the most usual entry format, which is uesd in
the following way:
\begin{verbatim}
\renewcommand\indexitem[2]{%
  \indexitemhang{0pt}%       First line left margin
                {10pt}%      Second, third...  lines left margin
                {}%          After entry if no locator
                {: }%        Entry-locator separator
                {#1}%        Entry
                {#2}}%       Locator
\end{verbatim}

Other macros are:
\begin{itemize}
\item \verb|\indexpreamble|, executed just after
  \verb|\begin{theindex}| (\verb|\relax| by default).
\item \verb|\indexpostamble|, executed before 
  \verb|\end{theindex}| (\verb|\relax| by default).
\item \verb|\indexskip|, which is \verb|\indexspace| by default, 
with similar purpose.
\item \verb|\indexheading|, which is added by |gindexh.ist| but no by
|gindex.ist|, is defined as follows:
\begin{verbatim}
\newcommand\indexheading[1]{%
  {\bfseries\hfil
   \MakeUppercase{#1}%
   \hfil}%
  \nopagebreak}
\end{verbatim}
\item \verb|\indexrangesep|, which by default is |-|.
\item \verb|\indexpagessep|, which by default is |, |.
\end{itemize}

Remember to set the style to |gindex| when running \textsf{makeindex}:
\begin{verbatim}
  makeindex -s gindex yourfile
\end{verbatim}
Or if you want |\indexheading|'s to be included:
\begin{verbatim}
  makeindex -s gindexh yourfile
\end{verbatim}

Note also there is usually no need to run \textsf{makeindex} to fine
tune the format.

\begin{example}
 With the following definitions, items and subitems are typeset, as
 usual, as separate paragraphs. However, if the item has no locator,
 and there is exactly one subitem, they are joined with a comma as
 separator (the code is somewhat low-level):
\begin{verbatim}
\renewcommand\indexitem[5]{%
  \def\next{%
    \indexitemhang{0pt}{20pt}{:}{, }{#1}{#2}%
    #3{#4}{#5}}%
  \ifnum\value{indexsubitems}=1\relax
    \ifx\\#2\\%
      \def\next{%
        \indexitemhang{0pt}{20pt}{:}{, }{#1, #4}{#5}}%
    \fi
  \fi
  \next}

\renewcommand\indexsubitem[2]{%
  \indexitemhang{0pt}{40pt}{}{, }{--- #1}{#2}}
\end{verbatim}
\end{example}

If an item starts with |\indexspecial|, what follows replaces the
current item.
\begin{example}
With |gindex.ist|, you can generate your own headings. If you are sure
there is nothing before |a '''| and |l '''| (actually, it can be
anything provided it is sorted at the right place), the following two
entries will ``group'' the items under two headings.
\begin{verbatim}
\index{a '''@\indexspecial\indexheading{a-k}}
\index{l '''@\indexspecial\indexheading{l-z}}
\end{verbatim}
\end{example}



\section{Internals}

The |ind| files is generated by |gindex.ist| with generic macros like:
\begin{verbatim}
  \addindexitem{bla1}{1}
    \addindexsubitem{subbla1}{3}
    \addindexsubitem{subbla2}{5}
\end{verbatim}
What \textsf{gindex} does is to convert them to the above format. Some
parameters should be cuntomized in the |ist| file, however. These are:
\begin{verbatim}
headings_flag   0
actual          '@'
quote           '"'
level           '!'
page_precedence "rRnaA"
keyword         "\\indexentry"
\end{verbatim}
As to |headings_flag|, its value is |-1| with |gindexh| and the
recommended way to deal with case is with |\indexheading|

\end{document}

MIT License
-----------

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