[XeTeX] XeTeX and luaTeX

[Arthur Reutenauer]

> In a recent thread here, luaTeX was said to be the intended eventual
> replacement for pdfTeX.

  This piece of information is based on earlier plans of the pdfTeX and
LuaTeX teams, when the intention was indeed that LuaTeX would become
pdfTeX 2.0 when it reached maturity.  Now the plans have changed
somewhat: pdfTeX development has been resumed by its original developer,
Hàn Thế Thành, while the pdfTeX developers from 1 or 2 years ago now
work mostly on LuaTeX; but it's not foreseen anymore the LuaTeX will be
a 100% compatible replacement for pdfTeX.

> Since luaTeX is Unicode-based, and handles OpenType fonts, what is the
> future of XeTeX? Will XeTeX continue to be developed?

  I leave it for Jonathan to answer that question, but I'm sure the
answer will be yes, to some extent :-)

>                                                       Should we be
> following and experimenting with luaTeX in anticipation of a move to
> that engine?

  If you're already using XeTeX and using its advanced features, I'd
really say no, you shouldn't anticipate a move to LuaTeX.  Note that the
latter is an extension of *pdfTeX*, not XeTeX, and is simply too
different from XeTeX with respect to OpenType font handling, Unicode,
etc.  LuaTeX and XeTeX have had completely different development paths
from the beginning (apart from their common origin as extensions of
Knuth's TeX), and they serve different needs.  I personally use both for
completely different purposes (through the macro package ConTeXt, not
LaTeX), and I don't envision abandoning either of them (basically: I
prefer XeTeX for documents with complex scripts and fonts, especially on
the Mac, and LuaTeX when I want to play with TeX's internal -- and the
language Lua, of course.  And sometimes I don't need any special
features, I can just use pdfTeX).

  The obvious question that is often raised in reaction to the opinion
expressed in the above paragraph is why there are no plans for merging
LuaTeX and XeTeX.  The simple answer is that the developers are already
busy enough as it is (and too few people); I'd also say that it might
not completely make sense on a technical level, for example because
XeTeX uses a lot of external libraries to implement its advanced
features, while LuaTeX leaves the same features to be implemented by the
macro package: it gives hooks into the TeX engine, whose parts can be
reprogrammed in Lua (by the user / macro package writer); what should a
"XeLuaTeX" program do?  This is not clear to me (I could imagine having
both options available in the engine, and choosing them with a switch
while typesetting, but then again, you can also make the same choice
before by simply deciding to use either of LuaTeX or XeTeX).

  This shouldn't of course discourage you from experimenting with
LuaTeX, especially now that it's easier to combine its advanced features
with LaTeX thanks to the lualatex-dev team :-)  But it's simply a
different program, in my opinion.

	Arthur