%%% Frank Mittelbach: is there a font?
% The following code allows to check, if some font (tfm metric) is available.

\batchmode
\font\X=<font name>%
\errorstopmode
 \ifx\X\nullfont
   <font not available>
 \else
   <use the font>
 \fi

% Having eTeX we can switch between modes using
% handy \interactionmode primitive.