[OS X TeX] Conditional typesetting engine selection

[Paul Vickers]

Hi

I am writing a document which I am typesetting in XeLaTeX using TeXshop 
2.03 on OS X Tiger 10.4.3. However, as the XeLaTeX engine is much slower 
on my PowerBook than LaTeX, for small updates I use the LaTeX engine for 
proofing purposes. I've set up a variable 'xetex':

\newif\ifxetex
\xetexfalse
%\xetextrue

Which, if true causes various XeLaTeX feaures to be enabled, otherwise 
the document reverts to vanilla LaTeX:
\ifxetex
  \usepackage{myxetexfonts}% My default XeLaTeX font settings
 
\newfontinstance\tabfontbf[Numbers=Monospaced,Weight=2,Scale=0.95]{Skia 
Regular}
  \newfontinstance\tabfont[Numbers=Monospaced,Scale=0.90]{Skia Regular}
  \newfontinstance\logo[Ligatures={Rare,Logos,Rebus,Diphthong}]{Palatino}
\newcommand{\applelogo}{\logo apple}

\else
    \usepackage[sc,osf]{mymathpazo}
    \usepackage[scaled]{helvet}
    \newcommand{\tabfontbf}{\bf}
    \newcommand{\tabfont}{}
    \newcommand{\applelogo}{}
\fi

now, I notice with TeXShop 2.03 I can add

     %!TEX TS-program = xelatex
     %!TEX encoding = UTF-8 Unicode
     %!TEX root = ./Main.tex

to the head of the document which will automatically select the XeLaTeX 
engine when I press the Typeset button. Being extraordinarily lazy, I 
would like to have the engine selected depending on the value of the 
variable 'xetex'. I have tried the following at the top of the document

\newif\ifxetex
\xetexfalse
%\xetextrue

\ifxetex
    %!TEX TS-program = xelatex
\else
    %!TEX TS-program = pdflatex
\fi
%!TEX encoding = UTF-8 Unicode
%!TEX root = ./Main.tex

However, this does not work. Is there any way to selectively set %!TEX 
TS-program from within a document?

Cheers

Paul
-- 
____________________________________
Dr P. Vickers BSc PhD CEng MIEE ILTM
Reader in Human-Computer Interaction &
Visiting Research Fellow of Loughborough University

School of Computing, Engineering, & Information Sciences
Northumbria University
Pandon Building, Camden Street
Newcastle-upon-Tyne
NE2 1XE

Tel +44 (0)191 243-7614
Fax +44 (0)870 133-9127
e-mail: paul.vickers at northumbria.ac.uk
web: www.paulvickers.com/northumbria

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