Practical use of Lua

Question

Although I always use LuaLaTeX to compile my documents, I don't really use Lua that often. Sometimes I even forget about it.

In my last document I used it to write a random word generator, which picks a word from a pool of words. Which can be really helpful in many different documents and circumstances. I came up with this code in another question, but I will repost it here, if someone wants to use it.

So today I asked myself, what are some other good uses for Lua in TeX documents? And here we go, now it's your turn to post your ideas.

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Thanks for all the great answers. There are some great ideas, and I certainly can put them to good use in my own documents (and other users aswell, I guess :) ). In my opinion, every answer deserves the check mark, so I guess I will let the community decide and choose the one with the most upvotes.

That of course doesn't mean you have to stop posting your awesome ideas ;)

Answer 1

LaTeX can not do all things you might want to typeset. Sometimes you might need the power of another (scripting) language. You are free to use Perl, PHP, bash scripts or what ever. But the main advantage of Lua is very simple - it's available. On all supported platforms. No need for the user to install anything else!

In my getmap package, I use a Lua script to connect web servers to download maps:

% compile with pdflatex -shell-escape
\documentclass{article}
\usepackage[latin1]{inputenc}
\usepackage{graphicx}
\usepackage{filecontents}
% use overwrite while optimizing the image
\usepackage[overwrite,mode=gm]{getmap}
\begin{document}
\begin{filecontents*}{berlin.epl}
&path=weight:5|color:purple|enc:_xq_IcgrpA?AFE@?^BFE@A^U@CLQXEZU?gCR?B?DBF@@?vA?D?D?BAHE@JBN@JLGFCG[DC~C?@?F?R?vA?p@iB@i@Fe@JWRSTOf@Gh@C^A?e@?gE?w@r@?lB@hA?`@??M?aA?]dI??O?O?Cn@cBfBeF|AeEHNVNBc@H@H_AEwA?OAMNA@N
\end{filecontents*}
\getmap[file=berlin, language=de, xsize=400, ysize=600,
        markers={&markers=size:mid|label:H|color:green|Berlin, Hbf
                 &markers=label:B|color:blue|Brandenburger Tor, Berlin},
        pathfile={berlin.epl}]{}
\includegraphics[width=6cm]{berlin}
\end{document}

The route was exported into a gpx file and converted to encoded polylines (Google's route format) by the very same Lua script:

getmapdl -m gpx2epl -G berlin.gpx

So, from my point of view, the embedded Lua interpreter opens new horizons!

Answer 2

The latest version of Tikz supports automatic graph layout with LuaTeX. When the appropriate TikZ options are given, a selection of Lua scripts are invoked that receive the structure of the graph and compute the positions of the nodes. A variety of automatic graph layout algorithms are supported. The API for writing your own algorithm in Lua is also documented in the manual. C/C++ is also supported through the runtime dynamic linking feature of Lua itself.

Example from the manual (note the layered layout option):

\documentclass[tikz]{standalone}
\usetikzlibrary{arrows.spaced,graphdrawing,graphs}
\usegdlibrary{layered}
\begin{document}
\tikz [nodes={text height=.7em, text depth=.2em,
              draw=black!20, thick, fill=white, font=\footnotesize},
       >=spaced stealth', rounded corners, semithick]
  \graph [layered layout, level distance=1cm, sibling sep=.5em, sibling distance=1cm] {
    "5th Edition" -> { "6th Edition", "PWB 1.0" };
    "6th Edition" -> { "LSX" [>child anchor=45], "1 BSD", "Mini Unix", "Wollongong", "Interdata" };
    "Interdata" -> { "Unix/TS 3.0", "PWB 2.0", "7th Edition" };
    "7th Edition" -> { "8th Edition", "32V", "V7M", "Ultrix-11", "Xenix", "UniPlus+" };
    "V7M" -> "Ultrix-11";
    "8th Edition" -> "9th Edition";
    "1 BSD" -> "2 BSD" -> "2.8 BSD" -> { "Ultrix-11", "2.9 BSD" };
    "32V" -> "3 BSD" -> "4 BSD" -> "4.1 BSD" -> { "4.2 BSD", "2.8 BSD", "8th Edition" };
    "4.2 BSD" -> { "4.3 BSD", "Ultrix-32" };
    "PWB 1.0" -> { "PWB 1.2" -> "PWB 2.0", "USG 1.0" -> { "CB Unix 1", "USG 2.0" }};
    "CB Unix 1" -> "CB Unix 2" -> "CB Unix 3" -> { "Unix/TS++", "PDP-11 Sys V" };
    { "USG 2.0" -> "USG 3.0", "PWB 2.0", "Unix/TS 1.0" } -> "Unix/TS 3.0";
    { "Unix/TS++", "CB Unix 3", "Unix/TS 3.0" } -> "TS 4.0" -> "System V.0" -> "System V.2" -> "System V.3";
};
\end{document}

Answer 3

LuaTeX provides all kinds of new hooks into the innards of TeX's operations. The paragraph-building algorithm, for one, has been opened up in several, very useful ways. This functionality enables the creation of new packages that do all kinds of stuff that simply wasn't possible before.

For instance, the selnolig package -- which performs selective suppression of typographic ligatures, for both German and English language texts, without the need for either tedious hand mark-up or the running of a pre-processor -- depends crucially on various LuaTeX callbacks to do its job. Without LuaTeX, this package would simply not exist. (Full disclosure: I'm the main author of this package.)

Answer 4

This may be thought of an extended comment to phg's answer. As an academic, I need to maintain multiple versions of my CV. For examples, one version of the CV must include all the publications, another should only include publications in the last five years, and another publications in the last six years! One should include a table that lists all grants and specify the amount of funding each year, the other only a list of grants with just the total amount mentioned. There are similar requirements for other fields of the CV.

In summary, the same data needs to be filtered differently and presented differently for each version. Manually maintaining multiple versions is an error-prone task. So, here is what I do (using ConTeXt):

1. All the data goes into different XML files. One file for publications, one for grants, etc. The advantage is that validate the data using standard XML tools.

2. Use the ConTeXt XML library to convert the XML file into Lua tables.

3. Create Lua functions to filter data from the Lua tables. For example, one function discards all publications that is more than n years old, another adds the grant amount for each year to compute the total amount, etc.

4. Create Lua functions to typeset according to each requirement. These are written in the CLD (ConTeXt Lua Document) format.

5. Now each version of the CV is easy to maintain. For example one has

   \startluacode
      cv.list_of_publications("journal", "all")
   \stopluacode
   

   while the other has

   \startluacode
      cv.list_of_publications("journal", 6)
   \stopluacode
   

   and so on.

In principle, it is possible to do all this by programming in TeX as well. After all, TeX is Turing complete. But it is much easier to do this with XML + Lua.

It is also possible to use any standard programming language to do this task. After all, every language has an XML parser, and CLD interface is easy to replicate with a well thought out TeX library. However, with such an interface all communication between the library and TeX takes place through text files. If something goes wrong, then debugging can be a pain. Ask anyone who has tried to debug why TeX labels do not appear in MP files!

Answer 5

Taking the question seriously, here are a few examples from the Context sources†:

• The new bibliography system, finally obsoleting Bibtex.
• The web server that powers the Pragma ADE website.
• Multi-purpose registers from which e. g. indices are derived.
• Various parsers for CSV, JSON and other common formats (for Latex provided by the lualibs package).
• A complete XML parser, the foundation of Context’s exceptional XML support.
• CLD -- you won’t believe how awesome it is until you try it. See also the wiki.
• The SQL interface..

• ... many more! I encourage you to explore the Context distribution. Particularly the directories

  • tex/context/base/
  • scipts/context/lua

  in the TEXMF.

† Note that much of the functionality is spread over multiple files. I only linked the entry points / main files in these cases.