[XeTeX] ifxetex package

[Bruno Voisin]

Le 19 juin 06 à 02:33, Will Robertson a écrit :

> LaTeX itself ensures than a package is only loaded once, and for
> Plain I've only added enough smarts that you at least shouldn't get
> error messages.

Hi Will,

I thought you would simply include, at the beginning of ifxetex.sty,  
the lines of code at the beginning of ifpdf.sty corresponding to the  
comments:

% Prevent reloading more than one:
[...]
%
% Package identification:
[...]
%
% Check, whether \ifpdf is already defined:
[...]
%

I'm not sure they are all absolutely necessary, but thought that they  
might perform checks general enough for inclusion, after minimal  
modification, in all packages testing for the use of a specific TeX  
engine.

In other words, perhaps a wider-ranging and longer-term solution  
would be having a general über-package ifengine containing a general  
infrastructure (all these general-purpose checks) plus engine- 
specific derivatives (ifpdf.sty, ifvtex.sty, ifxetex.sty), rather  
than separate packages ifpdf.sty, ifvtex.sty and ifxetex.sty each  
reimplementing the same functionality.

> Why would there be a version of XeTeX *without* the primitive
> \XeTeXversion?

\XeTeXversion was introduced in version 0.5 of XeTeX (I wasn't sure  
of exactly when it had been introduced, and checked at <http:// 
scripts.sil.org/cms/scripts/page.php? 
site_id=nrsi&item_id=xetex_history>). It's unlikely that versions  
prior to 0.5 are still out there in the wild, but Murphy's Law has  
unfortunately a tendency of reminding us of its existence at times  
(remember the foo-sys problems still very vivid on the OS X TeX list)!

Bruno