What can't TeX do?

Question

What are TeX's limitations in typography, book design and publishing? (and here TeX also includes all its derivatives, like pdfTeX, LuaTeX, and macro packages built upon it, LaTeX, ConTeXt etc.).

Some things (like math and references) are extremely easy in TeX. There are some things that are harder to do in TeX-based systems, but they are possible, even if cumbersome (like precise control of images' placement or manual control over layout and design). Solutions to some problems have been found (like microtype). Some things are rarely talked about (like color profiles).

Please mention what is either extremely hard to achieve with TeX or is not possible at all (due to inherent limitations of TeX, or due to bugs/limitations in the available tool chain). Please mention also which technological steps do not fit well with TeX workflow.

Answer 1

TeX has no real way to do river, lake and hole elimination. This would require a much more expensive paragraph layout algorithm than the Knuth and Plass dynamic programming.

Answer 2

The definitive answer to this is perhaps Donald Knuth's own answers, given in an earthshaking announcement in 2010 and recorded in this video and transcribed in the TUG journal, TUGboat, Volume 31 (2010), No. 2, pp121ff.

Answer 3

Some things that are perhaps possible in TeX (with some programming) but not built in LaTeX or plain TeX itself:

• Automatic paragraph flow around arbitrary shapes (like images)
• Autokerning based on the shape of the glyphs
• good multi column support (balancing, images/formulae crossing multiple columns)
• text areas with overflow capabilities ("read more on page 3")
• Output to an "open" format such as InDesign (for editing afterwards) or XML
• Some way of splitting a vbox at a point (should break an image in two parts for example)
• XML input
• This list could be continued, but you get the point: magazine layout is not easy in TeX

Answer 4

TeX does not perform a global optimization of its cost functions but does so on a page by page basis. While I think it might be possible to solve this without touching the kernel, this must be pretty hard to do efficiently and transparently and I am not aware of any package that has tried to do this.

For an example of the practical effects of this deficiency, see How to spread floats automatically over a whole chapter?

I stole this picture from there:

Answer 5

One of the things that are impossible in TeX90 is typesetting the first line of a paragraph in a different font than the rest of the para - with the possibility of hyphenation between the first and second line.

EDIT: It seems the magaz package implements this.

Answer 6

TeX was not really designed for fully automatic typesetting, as you may want when the source document is computer-generated (for things like database reports or equipment manuals), or needs to be typeset in many different page geometries. These things are possible, but they need some care. The main problem is that TeX wants to set beautiful paragraphs and if it can't do that, then it throws an overfull hbox and expects the author to deal with it (eg, by rewording the offending text, or marking additional hyphenation locations). Some discussion of lowering TeX's standards is in this FAQ answer, which will eliminate overfull boxes, but it's still true that TeX is at it's best at when beautiful paragraphs are possible.

Here's an example:

\documentclass{article}
\usepackage[text={3.01cm,8in}]{geometry}
\begin{document}
{%Help TeX not to give up too easily....
\tolerance=9999
\setlength{\emergencystretch}{1em}
TeX was not really designed for fully automatic typesetting, as you may want
when the source document is computer-generated (for things like database reports
or equipment manuals), or needs to be typeset in many different page geometries.\par}

%I'd rather see something like this
TeX was not\break really designed for\break fully automatic typesetting,
as you may want when the\break source document is computer-generated (for 
things like\break database reports or equipment manuals), or needs to be 
typeset in many different page geometries.
\end{document} 

Result:

Automatic breaking of displayed equations is another difficult aspect of automatic typesetting, although the breqn package makes an attempt at this.

Answer 7

Adding to the collection:

Q: How to undo \usepackage?

A: You can't.

To shamelessly copy and paste from the answer so that SX won't auto-comment my answer anymore:

Tex/Latex have what is called monolithic state: you can't cleanly isolate the configuration done by one package from another, which is one of the reasons why incompatibilities are possible. This means there is no way to identify how to undo what changes the \usepackage command has caused.

Answer 8

TeX, and Lua in LuaTeX are both Turing complete languages. So they should be able to do pretty much anything.

However, some things are more difficult due to the limited set of features of the language. Some other things require new algorithms, which may not perform reasonable well (say requiring $O(n^2)$ or even more computing times).

One particular example I can think of is grid typesetting. This is one thing I always wanted to do but haven't found any elegant solutions in the TeX world yet.

Answer 9

Automatic splitting of floats for a better overall look (https://tex.stackexchange.com/a/4682/13450).

This is of course related to the general problem of a lack of global optimization but more specific. It would be nice to have floating text environments (tables, listings, text boxes, subfigure collections ...) that were split into two smaller parts if this were to improve the overall layout of the document (footnotes already do something like this).

Answer 10

TeX and LaTeX is not really good at constructing dictionary-style texts.

It's really designed to expect tables and text as separate entities, and is not really good at flowing text from one minipage to another (like in magazines - continued on page ...).

One document i am writing at the moment, has a formatted set of formulae definitions, followed by a few paragraphs of text, and then a few more formulae, and then more text. I am currently doing this with the {tabbing} environment, with the \kill line set in the preface sections. It works, i suppose.

I'm still trying to get hanging numbers to work. Some places, such as running text, it is appropriate to use hanging numbers, rather than block numbers, but i can't see how to do this. I downloaded a package printnum where the documentation is in hanging numbers in the required style, but it's set to decimal, rather than twelfty.

Answer 11

Somewhat similar to Lev Bishop's answer: outputting the same file to different formats.

If I want to publish an article to arXiv, my HTML blog, a ePub book, and Git-whatever to accompany the code, I'll have a really long day with Pandoc and other tools instead of just iterating over targets such as PDF, HTML, ePub, Markdown.

As far as I understand, Tectonic aims to partially solve this problem.

Answer 12

Some miscellaneous points. They're mostly developer-oriented rather than user-oriented.

• Get the next token in the token list, in the general case. (fixed in LuaTeX)

  While there's \futurelet, it cannot distinguish between an implicit and an explicit character token.

  Check out implementation of \peek_analysis_map_inline:n in texdoc source3 for the difficulties (and even it can fail in some obscure cases).

• Check if two given tokens are equal in an expansion-only context in general case without "hardcoding" for each character. (fixed in LuaTeX)

• Some token list processing operations e.g. reversing a token list cannot be done in linear time if it's required to be expandable. (fixed in LuaTeX)

  (in my opinion, this is highly frustrating because it sometimes require developers to write somewhat contorted code if they want it to be usable)

• Get the current math style. expansion - \ThisStyle \SavedStyle painfully slow ... alternatives? - TeX - LaTeX Stack Exchange (partially fixed in LuaTeX with \Ustack, see link)

• Prefer ragged text to overfull hbox automatically _{(this point is somewhat similar to the fully automatic typesetting answer)}

Answer 13

As far as I remember, TeX is rather weak in prepress: imposition, bleed, trim, Flattermarke, paper thickness accommodation when folding (whatever it's called), etc.

So, basically, you cannot just take TeX output to printer and print your book directly from it.