[luatex] Luatex primitive names

[Manuel Pégourié-Gonnard]

Norbert Preining a écrit :
> On Mi, 11 Mär 2009, Manuel Pégourié-Gonnard wrote:
>> It will. Some services widely-used by mathematicians, such as ArXiv, still use
>> teTeX2, and some universities do so. People (esp. sysadmin) don't upgrade their
>> TeX system as frequently as we TeXies could wish. This is a fact.
> 
> But they will not *use* luatex. Yes, it will be present, but who will
> use it? Do you expect that ArXiv is switching to luatex, or any other of
> these systems?

Of course not. I just took the first well-known example of an *old* TeX system
still widely used today. The point is that today a lot years-old TeX systems are
still around, so I can't see any reason why some TL'08 will not be around in
2013 in some server in some university.

Now imagine, in 2013, a math student just beginning with LaTeX. He hears from a
friend that if he wants to have such or such great functionality (eg the latest
version of breqn heavily relying on LuaTeX) all he has to do is to put
\usepackage{breqn} in his preamble and compile with the pdflualatex command.
Hopefully, there is a pdflualatex button in the latest version of texworks he's
using at home on top of his brand new TL'13. He adds the line in his code,
clicks the button, everything works: hurray, he loves LaTeX!

Then he wants to compile his document on his university's servers, or send him
to a friend, still using and older TL. First, since the GUI there is not as
modern as his version, he doesn't use the correct command to compile. There the
macro package must be able to detect the problem and issue a meaningful error
message.

He finally manages to set the correct compilation command and tries to compile.
If his version of LuaTeX is too old and cannot run the latest version of breqn,
or breqn wants to adapt his code to an older syntax of equivalent primitives,
then the macro package needs to be able to detect the version and possibly issue
a meaningful error message.

All it takes to provide those meaningful error messages is a reliable mechanism
allowing macro writers to detect the engine and its version at runtime. And
providing such a mechanism costs essentially nothing.

Please note that in the above scenario no one is using LuaTeX before it becomes
 stable. The only assumption made is that there will still be pre-0.5 versions
around when 1.0 will be out. And I repeat: given the age of the TeX systems
still being used today, this case will most certainly happen.

Manuel.