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\startchapter[title={\CONTEXT\ in \TEXLIVE\ 2023}]

Starting with \TEXLIVE\ 2023 the default \CONTEXT\ distribution is \LMTX, a
follow up on \MKIV, running on top of the \LUAMETATEX\ engine instead of \LUATEX.
Already for a long time the \MKII\ version used with \PDFTEX, \XETEX\ and \ALEPH\
has been frozen and most users moved on from \MKIV\ to \LMTX\ (a more distinctive
tag for what internally is version \MKXL).

In principle one can argue that we now have three versions of \CONTEXT\ and there
can be the impression that they are very different. However, although \MKXL\ can
do more than \MKIV\ which can do more than \MKII, the user interface hasn't
changed that much and old functionality is available in newer versions. Of course
some old features make no sense in newer variants, like eight|-|bit font
encodings in an \OPENTYPE\ font realm and input encodings when one uses \UTF,
although we still support input encodings a.k.a.\ regimes. When we started using
the \type {Mk*} suffixes the main reason was that we had to distinguish files and
the official \TEX\ distribution doesn't permit duplicate file names. Using a
distinctive suffix also makes it possible to treat files differently.

\starttabulate[|T|c|c|c|Tl|]
\BC suffix \BC engine                           \BC template \BC arguments \BC main file \NC \NR
\HL
\NC MkII   \NC \PDFTEX, \XETEX, \ALEPH          \NC          \NC           \NC context.mkii \NC \NR
\HL
\NC MkIV   \NC \LUATEX, \LUAJITTEX, \LUAMETATEX \NC          \NC           \NC context.mkiv \NC \NR
\NC MkVI   \NC idem                             \NC          \NC   yes     \NC \NC \NR
\NC MkIX   \NC idem                             \NC   yes    \NC           \NC \NC \NR
\NC MkXI   \NC idem                             \NC   yes    \NC   yes     \NC \NC \NR
\HL
\NC MkXL   \NC \LUAMETATEX                      \NC          \NC           \NC context.mkxl \NC \NR
\NC MkLX   \NC idem                             \NC          \NC   yes     \NC \NC \NR
\stoptabulate

In this table \quote {template} files are a mix of \TEX\ and \LUA\ and originate
in the early days of \MKIV; basically, they are a wink to active server pages.
With \quote {arguments} we refer to files that accept named macro arguments which
means that they need to be preprocessed. That started as a proof of concept but
some core files are defined that way. Users will normally just use a \type {.tex}
file.

The \LUA\ files in the code base have the suffix \type {lua}, or when meant for
\LUAMETATEX\ that uses a newer \LUA\ engine they can have the suffix \type {lmt}.
There can also be \type {lfg} (font goodies) and \type {llg} (language goodies)
plus byte|-|compiled files with various suffixes but these are normally not seen
by users. We leave it at that.

So, while \TEXLIVE\ 2022 installed \MKII\ and \MKIV, \TEXLIVE\ 2023 installs
\MKIV\ and \LMTX. Therefore the most significant upgrade is in the engine that is
used by default: \LUAMETATEX\ instead of \LUATEX. The \MKII\ files are no longer
installed so we don't need \PDFTEX.

So how did we end up here? Initially the idea was that, because \LUATEX\ is
basically frozen, \LUAMETATEX\ would be the engine that we conduct experiments
with and from which occasionally we could backport code to \LUATEX. However it
soon became clear that this would not work out well so backporting is off the
table now. Just for the record: the project started years ago so we're not
talking about something experimental here. There have been articles in \TUGBOAT\
about what we've been doing over the years.

One of the first decisions I made when starting with \LUAMETATEX\ was to remove
the built|-|in backend, which then meant also removing the bitmap image inclusion
code. That made us get rid of dependencies on external libraries. In fact, a
proof|-|of|-|concept experimental variant didn't use the built|-|in backend at
all. The font loading code could be removed as well because that was not used in
\MKIV\ either. In \MKIV\ we also don't use the \KPSE\ library for managing files
so that code could be dropped from the engine tool; it can be loaded as
so|-|called optional library if needed but I'll not discuss that here. If you
look at what happens with the \LUATEX\ code base, you'll notice that updating
libraries happens frequently and that is not a burden that we want to impose on
users, especially because it also can involve updating build|-|related files.
Another advantage of not using them is that the code base remains small.

A direct consequence of all this was that the build process became much more
efficient and less complex. A fast compilation (seconds instead of minutes) meant
that more drastic experiments became possible, like most recently an upgrade of
the math subsystem. All this, combined with an overhaul of the code base, both
the \TEX\ and \METAPOST\ part, meant that backporting was no longer reasonable.
Being freed from the constraint that other macro packages might use \LUAMETATEX\
in turn resulted in more drastic experiments and adding features that had been on
our wish list for decades. Another side effect was that we could easily compile
native \MSWINDOWS\ binaries and immediately support transitions to \ARM|-|based
hardware.

Instead of \quotation {backporting after experimenting}, a leading motive became
\quotation {fundamentally move forward} while at the same time tightening the
relation between \CONTEXT\ and the engine: the engine code became part of the
distribution so that users can compile themselves, which fits perfectly in the
paradigm (and demands) of distributing all the source code, even that of the
engine. There is also less danger that patches on behalf of other usage
interferes with stable support for \CONTEXT. A specific installation is now more
or less long|-|term stable by design because it no longer depends on binaries
and|/|or libraries being provided for a specific platform and operating system
version. Of course installers and \TEXLIVE\ do provide the binaries, so users
aren't forced to worry about it, but they can move along with a system update by
recompiling an old, and for their purpose, frozen \CONTEXT\ code base.

An unofficial objective (or challenge) became that the accumulated source stays
around 12~\MB\ uncompressed, (compressed a bit over 2~\MB) and the binary around
3~\MB\ so that we could use the engine as an efficient \LUA\ runner as well as a
launcher stub, thereby removing yet another dependency. That way the official
\CONTEXT\ distribution didn't grow much in size. A bonus is that we now use the
same setup for all operating systems. It also opened up the possibility of a
exceptionally small installation with all bells and whistles included. Another
nice side effect, combined with automatic compilation on the compile farm, makes
that we can provide installations that reflect the latest state of affairs: a
recent binary combined with the latest \CONTEXT. As a result, most users quickly
went for \LMTX\ instead of \MKIV.

In the code base we avoid dependencies on specific platforms but there are a few
cases where the code for \MSWINDOWS\ and \UNIX\ differs. However, the
functionality should be the same. A good test is that for \MSWINDOWS\ we can
compile with mingw (cross|-|compilation), \MSVC\ (native) and clang (native);
that order is also the order of runtime performance. The native \MSVC\ binary is
the smallest but users probably don't care. In any case, it is nice to have a
fallback plan in place. The code is all in \CCODE; the \METAPOST\ code is
converted from \CWEB\ into \CCODE\ using a \LUA\ script but we also ship the
resulting \CCODE\ code. The code base provides a couple of \CMAKE\ files and
comes with a trivial build script.

When I say that there are no libraries used, I mean external libraries. We do use
code from elsewhere: adapted \type {avl} as well as \type {decnumber} (for the
\METAPOST\ library), adapted \type {hjn} (hyphenation), \type {miniz} (zip
compression), \type {pplib} (for loading \PDF\ files), \type {libcerf} (to
complement other math library support, but it might be dropped), and \type
{mimalloc} for memory management. However all the code is in the \LUAMETATEX\
code base and only updated after checking what changed. The most important
library originating elsewhere is of course \LUA: we use the latest and greatest
(currently) 5.4 release. We kept the \type {socket} library but it might be
dropped or replaced at some point. In addition there is a subsystem for
dynamically loading libraries; the main reason for that being that I needed \type
{zint} for barcodes, interfaces to sql databases, a bunch of compression
libraries, etc. But all that is tagged {\em optional} and \CONTEXT\ will never
depend on it. There are no consequences for compilation either because we don't
need the header files. The glue code is very minimalistic and most work gets
delegated to \LUA.

Initially, because the backend is written in \LUA, there was a drop in
performance of some 15\percent\ but that was stepwise compensated by gains in
performance in the engine and additional or improved functionality. The \CONTEXT\
code base is rather optimized so there was little to gain there, apart from using
new features. Existing primitive support could also be done a bit more
efficiently; it helps if one knows where potential bottlenecks are. Therefore, in
the meantime an \LMTX\ run can be quite a bit faster than a \MKIV\ run and it can
even outperform a \LUAJITTEX\ run. In practice, the difference between an
eight|-|bit \MKII\ run using the eight|-|bit \PDFTEX\ engine and a 32|-|bit
\LUAMETATEX\ run with \LMTX\ can be neglected, definitely on more complex
documents. I never get complaints about performance from \CONTEXT\ users, so it
might be a minor concern.

So what are the main differences in the installation? If you really want to
experience it you should use the standard installation. Currently the small
installer is the engine that synchronizes the installation over the net and,
assuming a reasonable internet connection, that takes little time. The
installation is relatively small, and many of the bytes used are for the
documentation. Updates are done by transferring only the changed files. The
\TEXLIVE\ installation is a bit larger because it shares for instance fonts with
the main installation and these come with resources used by other macro packages.
Both installations bring \MKIV\ as well as \LMTX\ and therefore provide \LUATEX\
as well as \LUAMETATEX. However, a \MKIV\ run is now managed by \LUAMETATEX\
because we use that engine for the runner. The \MKII\ code is no longer in
\TEXLIVE\ but is in the repositories and used to test and compare with \PDFTEX.
It just works.

The number of binaries and stubs is reduced to a minimum:

\starttabulate[|T|T||]
\BC file                           \BC symlink    \BC \NC \NR
\NC tex/texmf-platform/luametatex  \NC            \NC combined \TEX, \METAPOST\ and \LUA\ engine \NC \NR
\NC tex/texmf-platform/mtxrun      \NC luametatex \NC script runner, binary \NC \NR
\NC tex/texmf-platform/context     \NC luametatex \NC CONTEXT\ runner, binary \NC \NR
\NC tex/texmf-platform/mtxrun.lua  \NC            \NC script runner, lua code \NC \NR
\NC tex/texmf-platform/context.lua \NC            \NC loader for \CONTEXT\ runner \NC \NR
\NC tex/texmf-platform/luatex      \NC            \NC the good old ancestor \NC \NR
\stoptabulate

All of these programs are in the \CONTEXT\ distribution directory \typ
{tex/texmf-<platform>/}. In addition, \type {context} and \type {mtxrun} are
symlinks to the \type {luametatex} binary, where possible.

So, the \type {context} command runs \type {luametatex}, but loads the \LUA\ file
with the same name which in turn will locate the \CONTEXT\ management script
(\type {mtx-context}) in the \TEX\ tree and run it. The same is true for \type
{mtxrun}: it is a binary (link) that loads the script in (this time) the same
path and then can perform numerous tasks. For instance, identifying the installed
fonts so that they can be accessed by name is done with:

\starttyping
mtxrun --script font --reload
\stoptyping

Where in \MKII\ we had stubs for various utility scripts, already in \MKIV\ we
went for a generic runner and a bit more keying. It's not like these scripts are
used a lot and by avoiding shortcuts there is also little danger for a mixup with
the ever|-|growing list of other scripts in \TEXLIVE\ or commands that the
operating system provides.

The \LUATEX\ binary is optional and only needed if a user also wants to process
\MKIV\ files. There are no shell scripts used for launching. The two main calls
used by users are:

\starttyping
context foo.tex
context --luatex foo.tex
\stoptyping

A user has only to make sure that the binaries are in the path specification.
When you run from an editor, the next command does the work:

\starttyping
mtxrun --autogenerate --script context <filename>
\stoptyping

with \type {<filename>} being an editor|-|specific placeholder. Like other
engines, \LUAMETATEX\ (and \CONTEXT) needs a file database and format file, and
although it should generate these automatically you can make them with:

\starttyping
mtxrun --generate
context --make
\stoptyping

The rest of the installation is similar to what we always had and is \TDS\
compliant. The source code of \LUAMETATEX\ is included in the distribution itself
(which nicely fulfills the requirements) but can also be found at:

\starttyping
https://github.com/contextgarden/luametatex
\stoptyping

There are also some optional libraries there but \CONTEXT\ works fine without
them. The official latest distribution of \CONTEXT\ itself is:

\starttyping
https://github.com/contextgarden/context
https://github.com/contextgarden/context-distribution-fonts
\stoptyping

We see users grab fonts from the Internet and play with them. They can install
additional fonts in \typ {tex/texmf-fonts/data/<vendor>}. Project|-|specific
files can be collected in \typ {tex/texmf-project/tex/context/user/<project>}.
These directories are not touched by installations and can easily be copied or
shared between different installations. After adding files to the tree \typ
{mtxrun --generate} will update the file database.

In the distribution there are plenty of documents that describe how \LUAMETATEX\
with \LMTX\ differs from \MKIV\ with \LUATEX: new primitives, macro extensions,
more granular math rendering, improved memory management, new (or extended)
(rendering) concepts, more \METAPOST\ features; most is covered in one way or
another, and much is already applied in the \CONTEXT\ source code. After all, it
took a few years before we arrived here so you can expect substantial refactoring
of the engine as well as the code base, and therefore eventually there is (and
will be) more than in \MKIV.

When you compare a \CONTEXT\ installation with what is needed for other macro
packages you will notice a few differences. One concerns the way \TEX\ is
launched. An engine starts with a blank slate but can be populated with a
so|-|called format file that is basically a memory dump of a preloaded macro
package. So, the original way to process a file is to pass a format filename to
the engine. In order to avoid that a trick is used: when an engine (or
symlink|/|stub to it) is launched by its format name, the loading happens
automatically. So, for instance \type {pdflatex} is actually an equivalent for
starting \PDFTEX\ with the format file \typ {pdflatex.fmt} while \type {latex} is
\PDFTEX\ with another format file (\typ {latex.fmt}) starting up in \DVI\ mode.
And, as there are many engines, a specific macro package can have many such
combinations of its name and engine.

In \CONTEXT\ we don't do it that way. One reason is that we never distinguished
between backends: \MKII\ uses an abstract backend layer and load driver files at
runtime (it was one of the reasons why we could support \ACROBAT\ as soon as it
showed up, because we already supported the now obsolete but quite nice
\DVIWINDO\ viewer). And that model hasn't changed much as we moved on. Because we
use a runner, we also don't need to distinguish between engines: all formats have
the same name but sit on an engine subpath in the \TEX\ tree. Anyway, this
already removes quite some formats. On the other hand, \CONTEXT\ can be run with
different language specific user interfaces which means that instead of just
\type {context.fmt} we have \type {cont-en.fmt} and possibly more, like \type
{cont-nl.fmt}. So that can increase the number again but by default only the
English interface is installed. As a side note: where with \MKII\ we needed to
generate \METAPOST\ mem files, with its descendants having \MPLIB\ we load the
(actually quite a bit of) \METAPOST\ code at runtime. \footnote {Occasionally I
do experiments with loading the \TEX\ format code at runtime, but at this moment
the difference in startup time of about one second (assuming files are cached) is
too large and running over networks will be less fun, so the format file will
stay. The time involved in loading \METAPOST\ can be brought down but for now I
leave it as it is.}

In addition to a format file, for the \LUATEX\ and \LUAMETATEX\ engine we also
have a (small) \LUA\ loader alongside the format file. All this is handled by the
runner, also because we provide extensive command line features, and therefore of
no concern to users and package maintainers. However, it does make integrating
\CONTEXT\ in for instance \TEXLIVE\ different from other macro packages and
thereby puts an extra burden on the \TEXLIVE\ team. Here I want to thank the team
for making it possible to move forward this way, in spite of this rather
different approach. Hopefully a \LUAMETATEX\ integration is a bit easier in the
long run because we no longer have different stubs per platform and at least the
binary part now has no dependencies and only has a handful of files.

For those new to \CONTEXT\ or those who want to try it in \TEXLIVE\ 2023 there is
not much difference between the versions. However, \MKIV\ is now frozen and new
functionality only gets added to \LMTX. Of course we could backport some but with
most users already having moved on, it makes no sense. Just as we keep \MKII\
around for testing with \PDFTEX, we also keep \MKIV\ alive for testing with
\LUATEX. Maybe in a couple of years \MKIV\ will go the same route as \MKII:
ending up in the archives as an optional installation. \footnote {This text
appeared in \TUGBOAT\ around the 2023 \TEXLIVE\ release. Thanks to Karl Berry for
his careful reading and fixing of the text and of course for keeping \TEXLIVE\
alive.}

\stopchapter

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