use supp-fil in plain tex

[ecashin@coe.uga.edu (Ed L. Cashin)]

Hello.  I have a situation where I'd like to process an undetermined
number of figures in a TeX document.  The way I'm currently handling
it is by generating the TeX code with perl, with TeX code to include
each figure.

However, a much simpler and more general strategy, that might not be
much slower, would be to use a loop in the TeX code that included the
files if they were there.  

The task is made easier by the fact that the included files are
MetaPost figures with consecutive suffixes.  The loop, then has to do
this: 

      counter variable i = 1
      while exists file myfile.i
            include figure from myfile.i
            increment i
      done

I know that loops can be done in plain TeX with the \loop macro, and I
saw the "\doiffileelse" macro in supp-fil.tex.  I'm trying to use it
like this:

    \input supp-mis
    \input supp-fil

    \newcount\iterator\iterator=1
    \newif\ifNotDone\NotDonetrue

    \loop\ifNotDone
      \doiffileelse{sumvouch\iterator}
    	    {\placeFgBg{sumvouch.\iterator}\advance\iterator by 1}
    	    {\NotDonefalse}
    \fi\repeat

... which may or may not be the right way to write the loop, but I get
errors like this while supp-fil is loading:

   This is pdfTeX, Version 3.14159-13d (Web2C 7.3.1)
   (sumvouch.tex[/usr/local/teTeX/share/texmf/pdftex/config/pdftex.cfg]
   Babel <v3.6x> and hyphenation patterns for american, french, german, ngerman, n
   ohyphenation, loaded.
   (/usr/local/teTeX/share/texmf/tex/context/base/supp-mis.tex
   loading : Context Support Macros / Missing
   ) (/usr/local/teTeX/share/texmf/tex/context/base/supp-fil.tex
   loading : Context Support Macros / Files
   ! Incomplete \ifx; all text was ignored after line 77.
   <inserted text> 
   		   \fi 
   <to be read again> 
   		      \newread 
   l.77 \ifx\undefined\scratchread  \newread
   					     \scratchread  \fi

Is it possible to use supp-fil this way in order to make use of the
\doiffileelse macro in a plain tex source?

-- 
--Ed Cashin                     PGP public key:
  ecashin@coe.uga.edu           http://www.coe.uga.edu/~ecashin/pgp/