How do LaTeX3 and ConTeXt compare?

Question

As I understand it, LaTeX3 is a rewrite of LaTeX to fix the shortcomings of LaTeX2e, and ConTeXt is another TeX-based language (set of macros like LaTeX?) that solves quite a few problems that are hard to solve with LaTeX2e.

How do they compare? Do they solve the same problems? Does LaTeX3 bring to the LaTeX world similar functionalities as ConTeXt?

Answer 1

A full answer here has several parts. First, at the time of writing it's important to bear in mind that ConTeXt is not only available but works well, while LaTeX3 is a concept which is being developed. That means that it's not even 100% clear what shape LaTeX3 will take. It's also not clear that LaTeX3 will deliver, but for the purposes of answering the question I'll ignore this! I'll also highlight what seem to be (broad) similarities.

TeX-based systems

There are then two broad areas to talk about: the user 'experience' and the implementation. In both areas, there are differences but I'd like to highlight one important similarity: both ConTeXt and LaTeX3 are ultimately TeX-based. A radically-different approach from either would be to parse input using another language (Python is often highlighted, for its scripting ability), then convert to TeX primitives (plus low-level macros), and only do the real typesetting in TeX. Neither ConTeXt nor LaTeX3 do that.

At the user level

At the user level, LaTeX works with the concept of a document class as a key concept, .i.e. you always have:

\documentclass{<whatever>}

In LaTeX2e, the separation between a class and adding code is somewhat diffuse. The idea for LaTeX3 is to make 'design' and 'code' separate areas, and so have the document class as a purely design concept. ConTeXt does not enforce the idea of a loading a particular 'style' for a document in the same way (although it is possible to load a module to set defaults). There is a key philosophical difference here, as ConTeXt is in many ways closer to the plain TeX concept of 'author as designer', while LaTeX3 is intended to enhance the separation of the two roles.

An area where there is clear similarity is that LaTeX3 will make a lot more use of keyval input 'out of the box' than LaTeX2e does. This is very much a similarity to ConTeXt, which makes extensive use of keyval. There are, however, differences in implementation (the classic one is that LaTeX keyval input skips spaces around the =, while ConTeXt does not).

Another similarity in this area is that the scope of 'core' LaTeX3 supported ideas is intended to be much broader than 'core' LaTeX2e ones, and thus similar to what ConTeXt manages. Quite how this works out depends on the development of LaTeX3, do it is not possible at this stage to give a more detailed analysis of this area. This area encompasses the 'limitations of LaTeX2e' part of the question. For example, ConTeXt can do proper grid typesetting, which is a significant challenge in LaTeX2e.

Implementation

At the implementation level, ConTeXt (Mark IV) uses a mix of TeX and Lua. On the other hand, LaTeX3 is (currently) dependent on e-TeX plus the \pdfstrcmp macro (or equivalent functionality), and thus works with suitably recent versions of pdfTeX, XeTeX and LuaTeX. LaTeX3 then constructs a programming language of its own ('expl3') using the require TeX primitives. This is clearly a fundamental different, as Lua provides ConTeXt with a flexible programming system and also access to TeX internals that are not available using primitives. At the time of writing, it's not clear how LaTeX3 might handle 'LuaTeX-only' ideas: might there be team-supported 'LuaTeX-only' modules, for example?

The fact that LaTeX3 uses only TeX, whereas ConTeXt uses a large amount of Lua, leads on to the fact that LaTeX3, like LaTeX2e, is intended to be a TeX format which can be used in a 'classical' manner

pdftex "&latex3" <myfile>

ConTeXt, in contrast, is a more 'dynamic' assembly as the Lua part is not saved into the format file. Thus ConTeXt is always executed using the context script. Using this script-based wrapper, ConTeXt can deal with multiple TeX runs, indexing and so forth 'automagically'. The intention (at present) is that LaTeX3 will work in the same way as LaTeX2e: one LaTeX run = one TeX run.

Documenting interfaces

ConTeXt is build explicitly on TeX and Lua, while LaTeX3 defines its own language, expl3. Thus programming ConTeXt means programming in TeX, which is not documented formally in the ConTeXt manuals. A key driver behind LaTeX3 is the idea that beyond the kernel, everything needed to program LaTeX3 should be documented in the LaTeX3 documentation.

LaTeX3 is also aiming for a clear separation between user functions and internal functions, i.e. for every document-level function \foo there should be a (documented) internal function \int_foo. ConTeXt has a very rich set of interfaces, but is not (to my knowledge) built on quite such strict 'two-layer' principles.

Answer 2

ConTeXt is a complete, self contained system which tries to have solutions for (almost) everything.

LaTeX (all versions) on the other side is "only" a kernel. That you need to load packages to get some features is not a deficiency: LaTeX is meant to be extended by packages and classes. LaTeX3 will move some basic features which are currently in packages to the kernel, nevertheless a lot will have to be added by other package/class writers. source3 or xparse define mostly basic functions meant for package writers.

ConTeXt is managed by (and so under control) a rather small team. (I have no idea what would happen if the principal maintainer (Hans Hagen) would stop the work on ConTeXt.)

The LaTeX team is larger and has evolved over the time. Some people did quit the team, new people joined.

There exist up to no documentation about the inner working and ideas of the implementation ConTeXt. That makes it rather difficult to write yourself code to extend or change ConTeXt. ConTeXt has a concept of "user modules" but I don't think it is used much (and as the maintainer once wrote "The fact that it's custom in LaTeX to overload code and thus create a maintenance decency does not mean that I want such a dependency on my code."). My impression is that in most cases people wait until a feature is implemented by the ConTeXt maintainers.

On the other side there exist hundreds and thousands of page of internal LaTeX documentation. If you look at the documentation of e.g. source3 you see that the LaTeX team make a large effort to describe the ideas behind the code and every time you ask something you get long and useful answers. LaTeX don't only allow you to take part you are actually invited to add something to LaTeX.

I think ConTeXt is very powerful and someone who wants only a good system to write/manipulate documents should consider it. But for me part of the fun of TeX is the ability to write my own code, to debug problems, to understand the working of the system. I don't want to use only applications where I simply have to learn which button to press or which command to type even if this application can do everything I want and so every time I personally tried to find my way in ConTeXt I was at the end frustrated.