%D \module
%D   [       file=syst-tex,
%D        version=1999.03.17,  % an oldie: 1995.10.10
%D          title=\CONTEXT\ System Macros,
%D       subtitle=Efficient \PLAIN\ \TEX\ loading,
%D         author=Hans Hagen,
%D           date=\currentdate,
%D      copyright={PRAGMA / Hans Hagen \& Ton Otten}]
%C
%C This module is part of the \CONTEXT\ macro||package and is
%C therefore copyrighted by \PRAGMA. See licen-en.pdf for 
%C details. 

%D We've build \CONTEXT\ on top of \PLAIN\ \TEX. Because we 
%D want to make the format file as independant as possible of 
%D machine dependant font encodings, we have to bypass the 
%D loading of fonts. 
%D 
%D Let's start at the beginning. Because \PLAIN\ is not yet
%D loaded we have to define some \CATCODES\ ourselves. 

\catcode`\{=1 % left brace is begin-group character
\catcode`\}=2 % right brace is end-group character
\catcode`\#=6 % hash mark is macro parameter character
\catcode`\^=7 % circumflex is for superscripts

%D To prevent all kind of end||of||file problems, for the 
%D moment we simply ignore the Control~Z token. 

\catcode`\^^Z=9

%D We are going to report to the user what we are skipping.

\def\skipmessage#1{\immediate\write16{skipping #1 in plain}} 

%D We want to be able to use the \type{\newsomething}
%D declarations not only on the \type{\outer} level. This can
%D be done by redefining \type{\outer} so we have to save its
%D original meaning. 

\let\normalouter = \outer       
\let\outer       = \relax

%D We also want to postpone the loading of hyphenation patters,
%D so we redefine and therefore save \type{\input}. 

\let\normalinput = \input  
\def\input       #1 {\skipmessage{\string\input}}

%D Finaly are going to we redefine some font specification 
%D commands and that's why we save them too. The redefinitions
%D are straightforward because the macros have to do nothing 
%D but skipping.

\let\normalskewchar         = \skewchar
\def\skewchar               #1=#2 {\skipmessage{\string\skewchar}}

\let\normaltextfont         = \textfont
\let\normalscriptfont       = \scriptfont
\let\normalscriptscriptfont = \scriptscriptfont

\def\textfont               #1=#2{\skipmessage{\string\textfont}}
\def\scriptfont             #1=#2{\skipmessage{\string\scriptfont}}
\def\scriptscriptfont       #1=#2{\skipmessage{\string\scriptscriptfont}}

%D The redefinition of \type{\font} is a bit more complicated, 
%D because in version 3.14159 a scaled specification was 
%D introduced. 

\let\normalfont = \font

\def\skipscaled scaled #1 {}

\long\def\font#1=#2 #3%
  {\ifx#3s%
     \skipmessage{scaled \string\font}%
     \let\next=\skipscaled
   \else
     \skipmessage{\string\font}%
     \let\next=\relax
   \fi
   \next#3}

%D Relaxing some font switching macros is needed because we 
%D don't want any error messages during loading. These 
%D unharmfull messages could be ingored. 
%D
%D The next substitution is needed for determining 
%D \type{\p@renwd} in the macro \type{\bordermatrix}. 

\def\tenex#1%
  {\skipmessage{used \string\tenex}\hskip8.75002pt} 

%D We need to define \type{\tenrm} for switching to 
%D \type{\rm}. 

\def\tenrm%
  {\skipmessage{\string\tenrm}} 

%D In \CONTEXT\ all \PLAIN\ \TEX\ fonts are available, just 
%D like \type{\p@renwd}. We only postpone loading them until
%D they are actually needed.

%D By bypassing fonts, some definitions become less valid so 
%D we have to redefine them afterwards. 
%D 
%D \starttypen
%D \let\normalbordermatrix=\bordermatrix
%D 
%D \def\bordermatrix%
%D   {\bgroup
%D    \setbox0=\hbox{\getvalue{\textface\c!mm\c!ex}B}%
%D    \global\p@renwd=\wd0\relax
%D    \egroup
%D    \normalbordermatrix}
%D \stoptypen

%D Now we are ready for loading \PLAIN\ \TEX. Of couse we use 
%D \type{\normalinput} and not \type{\input}.

\normalinput plain.tex \let\normalfmtversion\fmtversion

%D We have to take care of unwanted \PDFTEX\ 
%D initializations. We just want to default to \DVI\ output. 

\ifx\pdftexversion\undefined 
  \newcount\pdfoutput
\else
  \pdfoutput=0
\fi 

%D When applicable, we also load the \ETEX\ source and 
%D defintion files. 

\bgroup \obeylines 

\ifx\eTeXversion\undefined 

  \long\gdef\beginETEX#1\endETEX%
    {}

  \gdef\beginTEX% 
    {\bgroup\obeylines\dobeginTEX}

  \gdef\dobeginTEX#1 
    {\egroup}

  \global\let\endTEX\relax

\else

  \long\gdef\beginTEX#1\endTEX%
    {}

  \gdef\beginETEX% 
    {\bgroup\obeylines\dobeginETEX}

  \gdef\dobeginETEX#1 
    {\egroup\immediate\write16%
       {line \the\inputlineno: inserting E-TEX code \detokenize{#1}}}

  \global\let\endETEX\relax

\fi 

\egroup

%D Well, this redefintion of \type {\input} fails on \ETEX, 
%D because of some \type {\cs\fi} construts. So now we use:

\beginETEX etex.src etexdefs.lib 

  \def\input#1%
    {\bgroup
     \skipmessage{\string\input}%
     \expandafter\ifx\expandafter#1\csname l@ngdefnfile\endcsname    
       \let\input\egroup
     \else
       \def\input##1 {\egroup}%
     \fi
     \input}

  \normalinput     etex.src \relax 
  \normalinput etexdefs.lib \relax 

  \let\fmtversion\normalfmtversion

\endETEX

\let\normalprotected  = \protected
\let\normalunexpanded = \unexpanded

%D We restore some redefined primitives to their old meaning. 

\let\font             = \normalfont
\let\skewchar         = \normalskewchar
\let\textfont         = \normaltextfont
\let\scriptfont       = \normalscriptfont
\let\scriptscriptfont = \normalscriptscriptfont
\let\input            = \normalinput
\let\outer            = \normalouter

%D We reset some of the used auxiliary macro's to 
%D \type{\undefined}. One never knows what testing on them is
%D done elsewhere. 

\let\skipmessage            = \undefined
\let\skipscaled             = \undefined
\let\normalfont             = \undefined
\let\normalskewchar         = \undefined
\let\normaltextfont         = \undefined
\let\normalscriptfont       = \undefined
\let\normalscriptscriptfont = \undefined
\let\normalinput            = \undefined
\let\normalouter            = \undefined

%D We want a bit more statistics and some less logging info 
%D in the \type{log} file. 

\def\wlog#1{} 

%D To prevent clashes, we slightly redefine the phantom 
%D macros: we let them hide their behaviour by grouping. 

\catcode`@=11

%D Somehow this one does not work ok in math mode:

\def\ph@nt%
  {\bgroup
   \ifmmode
     \expandafter\mathpalette\expandafter\mathph@nt
   \else
     \expandafter\makeph@nt
   \fi}

\def\finph@nt%
  {\setbox\tw@\null
   \ifv@ \ht\tw@\ht\z@ \dp\tw@\dp\z@ \fi
   \ifh@ \wd\tw@\wd\z@ \fi 
   \box\tw@
   \egroup}

%D But this one does work. 

\def\ph@nt%
  {\ifmmode
     \expandafter\mathpalette\expandafter\mathph@nt
   \else
     \bgroup\expandafter\makeph@nt
   \fi}

\def\finph@nt%
  {\setbox\tw@\null
   \ifv@ \ht\tw@\ht\z@ \dp\tw@\dp\z@ \fi
   \ifh@ \wd\tw@\wd\z@ \fi 
   \box\tw@
   \ifmmode\else\egroup\fi}

\catcode`@=12

%D Just for tracing purposes wet set:

\tracingstats=1

\endinput
