%D \module
%D   [       file=enco-ini,
%D        version=1998.12.03,
%D          title=\CONTEXT\ Encoding Macros,
%D       subtitle=Initialization,
%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. Non||commercial use is
%C granted.

% \everyuppercase
% \dotlessi
% single/double quotes 
% hyphens 
% characterencoding  => encoding 
% charactermapping => mapping 

%D Most of this module used to be part of the font and language
%D modules. While implementing Czech support, I decided to
%D isolate this code.

%D While dealing with input (the text source) and output (the
%D glyphs), encoding comes into view. To summarize a few:
%D
%D \startopsomming
%D \som  Bytes in the input file are mapped to an internal
%D       representation. An~\type {a} often stays an~\type {a},
%D       but~\type {\"e} can become either one code or become
%D       two codes (ending in overlapping glyphs).
%D \som  Characters can be made active and mapped onto another
%D       character.
%D \som  When changing case, characters are mapped onto
%D       themselves, their case||counterpart or a reasonable
%D       alternative, like~\"e onto~e.
%D \som  Single character representations in a \DVI\ file can 
%D       be mapped onto one or more characters, either of not
%D       in more than one font file (virtual fonts).
%D \som  In the final format, fonts collections can be 
%D       partially embedded, thereby losing the one||to||one 
%D       relation between several instances of one font.
%D \som  For special purposes, individual characters should be
%D       mapped onto a dedicated encoding vector, for instance
%D       \PDF\ document encoding.
%D \stopopsomming
%D
%D These and other kind of mappings are to be dealt with, and
%D the exact way of dealing often depends on the language to be
%D typeset.

\writestatus{loading}{Context Encoding Macros (ini)}

\unprotect 

\startmessages  dutch  library: encodings
  title: encoding
      1: codering --
      2: codering -- wordt geladen
      3: onbekende codering --
\stopmessages

\startmessages  english  library: encodings
  title: encoding
      1: coding --
      2: coding -- is loaded
      3: unknown coding --
\stopmessages

\startmessages  german  library: encodings
  title: Kodierung
      1: Kodierung --
      2: Kodierung -- ist geladen
      3: Unbekannte Kodierung --
\stopmessages

%D First we define a few local constants. 

\def\@map@   {@m@ap@} % mapping prefix 
\def\@plain@ {@e@pl@} % plain TeX encoding vector

%D \macro 
%D   {useencoding}
%D
%D Encodings things are defined in separate files and are 
%D loaded only once, using: 
%D
%D \showsetup{\y!useencoding}

\def\douseencoding#1%
  {\doifundefined{\c!file\f!encodingprefix#1}%
     {\setvalue{\c!file\f!encodingprefix#1}{}%
      \makeshortfilename[\f!encodingprefix#1]%
      \startreadingfile
      \readsysfile{\shortfilename}
        {\showmessage{\m!encodings}{2}{#1}}
        {\showmessage{\m!encodings}{3}{#1}}%
      \stopreadingfile}}

\def\useencoding[#1]%
  {\processcommalist[#1]\douseencoding}

%D \macros
%D   {startmapping,usemapping}
%D
%D In order to process patterns, convert from lower to
%D uppercase and vise versa and some more, we provide a
%D mechanism to define mappings. The first real application
%D of this command was:
%D
%D \starttypen
%D \startmapping [something]
%D   \definecasemap 165 181 165   
%D   \definecasemap 171 187 171   
%D   ...
%D   \defineuppercasecom \i  {I} 
%D   \defineuppercasecom \l  \L 
%D   \definelowercasecom \AE \ae
%D   ...
%D \stopmapping
%D \stoptypen
%D
%D So, character 165 becomes 181 in uppercase and 165 in 
%D lowercase. A mapping is activated with \type {\usemapping}.

\def\startmapping[#1]%
  {\pushmacro\charactermapping
   \def\charactermapping{#1}%
   \doifundefined{\@map@\charactermapping}
     {\expanded{\newtoks\csname\@map@\charactermapping\endcsname}}}

\def\stopmapping%
  {\popmacro\charactermapping}

\def\setmappingtoks%
  {\@EA\let\@EA\mappingtoks\csname\@map@\charactermapping\endcsname}

\def\definecasemap #1 #2 #3 % code lower upper
  {\setmappingtoks
   \appendtoks\setcasemap #1 #2 #3 \to\mappingtoks
   \ignorespaces}

\def\setcasemap #1 #2 #3 %
  {\catcode#1=\@@letter 
   \lccode #1=#2 
   \uccode #1=#3 }

\def\definespacemap #1 #2 % code sfcode
  {\setmappingtoks
   \appendtoks\setspacemap #1 #2 \to\mappingtoks
   \ignorespaces}

\def\setspacemap #1 #2 %
  {\catcode#1=\@@other  
   \lccode #1=0 
   \uccode #1=0 
   \sfcode #1=#2 } 

\def\defineuppercasecom#1#2% 
  {\setmappingtoks
   \appendtoks\setuppercasecom#1{#2}\to\mappingtoks
   \ignorespaces}

\def\definelowercasecom#1#2% 
  {\setmappingtoks
   \appendtoks\setlowercasecom#1{#2}\to\mappingtoks
   \ignorespaces}

\let\setuppercasecom\gobbletwoarguments
\let\setlowercasecom\gobbletwoarguments

\def\setcasecom#1#2{\def#1{#2}}

\def\usemapping[#1]%
  {\doifdefined{\@map@#1}{\the\csname\@map@#1\endcsname}}

%D Further on we have to take some precautions when dealing
%D with special characters like~\type{~}, \type{_}
%D and~\type{^}, so let us define ourselve some handy macros
%D first.

\def\protectfontcharacters%
  {\edef\unprotectfontcharacters%
     {\catcode`\noexpand ~=\the\catcode`~\relax
      \catcode`\noexpand _=\the\catcode`_\relax
      \catcode`\noexpand ^=\the\catcode`^\relax}%
   \catcode`~=\@@letter
   \catcode`_=\@@letter
   \catcode`^=\@@letter\relax}

% \def\unprotectfontcharacters%
%   {\catcode`\~=\@@active
%    \catcode`\_=\@@subscript
%    \catcode`\^=\@@superscript\relax}}

%D The completeness of the Computer Modern Roman typefaces
%D makes clear how incomplete other faces are. To honour 7~bit
%D \ASCII, these fonts were designed using only the first 127
%D values of the 256 ones that can be presented by one byte.
%D Nowadays 8~bit character codings are more common, mainly
%D because they permit us to predefine some composed
%D characters, which are needed in most european languages.
%D
%D Supporting more than the standard \TEX\ encoding vector
%D |<|which in itself is far from standard and differs per
%D font|>| puts a burden on the fonts mechanism. The \CONTEXT\
%D mechanism is far from complete, but can handle several
%D schemes at once. The main problem lays in the accented
%D characters and ligatures like~ff, although handling
%D ligatures is not the responsibility of this module.
%D
%D By default, we use \PLAIN\ \TEX's approach of placing
%D accents. All other schemes sooner or later give problems
%D when we distribute \DVI||files are distributed across
%D machines and platforms. Nevertheless, we have to take care
%D of different encoding vectors, which tell us where to find
%D the characters we need. This means that all kind of
%D character placement macro's like \type{\"} and \type{\ae}
%D have to be implemented  and adapted in a way that suits
%D these vectors.
%D
%D The main difference between different vector is the way
%D accents are ordered and/or the availability of prebuilt
%D accented characters. Accented characters can for instance be
%D called for by sequences like \type{\"e}. Here the \type{\"}
%D is defined as:
%D
%D \starttypen
%D \def\"#1{{\accent"7F #1}}
%D \stoptypen
%D
%D This macro places the accent \accent"7F {} on top of an~e
%D gives \"e. Some fonts however can have prebuild accents and
%D use a more direct approach like
%D
%D \starttypen
%D \def\"#1{\if#1e\char 235\else ... \fi}
%D \stoptypen
%D
%D The latter approach is not used in \CONTEXT, because we
%D store relevant combinations of accents and characters in
%D individual macros.

%D We define character substitutes and commands with definition
%D commands like:
%D
%D \starttypen
%D \startcoding[texnansi]
%D
%D \defineaccent " a           228
%D \defineaccent ^ e           234
%D \defineaccent ' {\dotlessi} 237
%D
%D \definecharacter ae 230
%D \definecharacter oe 156
%D
%D \definecommand b \texnansiencodedb
%D \definecommand c \texnansiencodedc
%D
%D \stopcoding
%D \stoptypen
%D
%D The last argument of \type{\defineaccent} and
%D \type{\definecharacter} tells \TEX\ the position of the
%D accented character in the encoding vector. In order to
%D complish this, we tag each implementation with the character
%D coding identifier. We therefore need two auxiliary variables
%D \type{\characterencoding} and \type{\nocharacterencoding}. These
%D contain the current and default encoding vectors and both
%D default to the \PLAIN\ one.

\let\characterencoding   = \@plain@
\let\nocharacterencoding = \@plain@
\let\charactermapping    = \@plain@

%D \macros
%D   {startcoding, setcoding}
%D
%D Before we can redefine accents and special characters, we
%D have to tell \CONTEXT\ what encoding is in force. The next
%D command is responsible for doing this and also takes care of
%D the definition of the recoding commands. We use the \type 
%D {\start}||\type {\stop}||commands for definitions and the 
%D \type {\set}||command for local switching. 

\def\donthandleaccent#1#2%
  {\getvalue{\characterencoding#1\string#2}}

\def\startcoding[#1]%
  {\doifelsenothing{#1}
     {\let\stopcoding\relax}
     {%\protectfontcharacters % problematic in language loading
      \showmessage{\m!encodings}{1}{#1}%
      \pushmacro\dohandleaccent
      \let\dohandleaccent\donthandleaccent
      \def\characterencoding{@#1@}%
      \def\stopcoding%
        {\popmacro\dohandleaccent
         \let\characterencoding=\@plain@
         \unprotectfontcharacters}}} % ?? 

\def\setcoding[#1]% use grouped! 
  {\doifsomething{#1}
     {\let\dohandleaccent\donthandleaccent
      \def\characterencoding{@#1@}%
      \enablelanguagespecifics[\currentlanguage]}}

\def\startencoding{\startcoding}
\def\stopencoding {\stopcoding}
\def\setencoding  {\setcoding}

%D The use of these macros are not limited to font 
%D definition files, but may also be used when loading 
%D patterns. 

%D \macros
%D   {defineaccent, definecharacter, definecommand}
%D
%D The actual definition of accents, special characters and
%D commands is done with the next three commands.

\def\defineaccent%
  {\protectfontcharacters
   \dodefineaccent}

\def\dodefineaccent#1 #2 %
  {\unprotectfontcharacters
   \dododefineaccent#1 #2 }

\def\dododefineaccent#1 #2 #3 %
  {\doifnumberelse{#3}
     {\setvalue{\characterencoding#1\string#2}{\char#3}}
     {\setvalue{\characterencoding#1\string#2}{#3}}%
   \unprotectfontcharacters}

\def\definecharacter#1 #2 %
  {\doifnumberelse{#2}
     {\setvalue{\characterencoding\string#1}{\char#2}}
     {\setvalue{\characterencoding\string#1}{#2}}}

%D Instead of numbers, a command may be entered.

\def\definecommand#1 #2 %
  {\setvalue{\characterencoding\string#1}{#2}}
 
%D Here we see that redefining accents is characters is more
%D or less the same as redefining commands. We also could have
%D said:
%D
%D \starttypen
%D \def\defineaccent#1 #2 {\definecommand#1\string#2 \char}
%D \def\definecharacter#1 {\definecommand#1 \char}
%D \stoptypen

%D \macros
%D   {redefineaccent}
%D
%D Telling \CONTEXT\ how to treat accents and special
%D characters is a two stage process. First we signal the
%D system which commands are to be adapted, after which we can
%D redefine their behavior when needed. We showed this in the
%D previous paragraphs. These redefinitions are grouped at the
%D end of this file, but we show some examples here.
%D
%D Accents or accent generating commands are redefined by:
%D
%D \starttypen
%D \redefineaccent  '  % grave
%D \redefineaccent  "  % dieresis
%D \redefineaccent  ^  % circumflex
%D \redefineaccent  v  % caron
%D \stoptypen
%D
%D The original \PLAIN\ \TEX\ meaning of each accent generating
%D command is saved first. Next these commands are redefined to
%D do an indirect call to a macro that acts according to the
%D encoding vector in use.

\def\redefineaccent%
  {\protectfontcharacters
   \doredefineaccent}

\def\doredefineaccent#1 %
  {\def\!!stringa{\nocharacterencoding\string#1}%
   \doifundefined{\!!stringa}
     {\@EA\letvalue\@EA\!!stringa\@EA=\csname\string#1\endcsname}%
   \setvalue{\string#1}{\dohandleaccent#1}%
   \unprotectfontcharacters}

%D \macros
%D   {defineaccentcommand}
%D
%D When needed, one can overload the default positions of the
%D accents. The \PLAIN\ \TEX\ defaults are: 
%D
%D \starttypen
%D \defineaccentcommand `  18
%D \defineaccentcommand '  19
%D \defineaccentcommand v  20
%D \defineaccentcommand u  21
%D \defineaccentcommand =  22
%D \defineaccentcommand ^  94
%D \defineaccentcommand .  95
%D \defineaccentcommand H 125  % "7D 
%D \defineaccentcommand ~ 126  % "7E 
%D \defineaccentcommand " 127  % "7F 
%D \stoptypen

\def\defineaccentcommand%
  {\protectfontcharacters
   \dodefineaccentcommand}

\def\dodefineaccentcommand#1 #2 %
  {\doifnumberelse{#2}
     {\setvalue{\characterencoding\string#1}##1{{\accent#2 ##1}}}
     {\setvalue{\characterencoding\string#1}##1{{#2##1}}}%
   \unprotectfontcharacters}

%D We don't have to define them for the default \PLAIN\ case. Commands 
%D may be used instead of character codes. 

%D \macros
%D   {normalaccent}
%D
%D The next (in fact three) macros to take care of \type{\"e}
%D as well as \type{\"{e}} situations. The latter one is always
%D handled by \TEX's \type{\accent} primitive, but the former
%D one can put the accents on top of characters as well as use
%D \type{\char} to call for a character directly.

% kan met minder def's en \expandafter...

\let\normalaccent=\accent

\unexpanded\def\dohandleaccent#1%
  {\def\dodohandleaccent%
     {\ifx\next\bgroup
        \def\next{\getvalue{\nocharacterencoding#1}}%
      \else
        \def\next{\dododohandleaccent#1}%
      \fi
      \next}%
   \futurelet\next\dodohandleaccent}

\def\dododohandleaccent#1#2%
  {\bgroup
   \ifundefined{\characterencoding#1\string#2}%
     \def\\{\getvalue{\nocharacterencoding#1}#2\egroup}%
   \else
     \def\\{\getvalue{\characterencoding#1\string#2}\egroup}%
   \fi
   \\}

%D The trick with \type{\\} is needed to prevent spaces from
%D being gobbled after the accented character, should we have
%D \type{\next}, we should have ended up with gobbled spaces.

%D \macros
%D   {redefinecommand}
%D
%D Redefinition of encoding dependant commands like \type{\b}
%D and \type{\c} can be triggered by:
%D
%D \starttypen
%D \redefinecommand  b  % something math
%D \redefinecommand  c  % something math
%D \stoptypen
%D
%D Handling of characters is easier than handling accents
%D because here we don't have to take care of arguments. We
%D just call for the right glyph in the right place.
%D
%D The \type{\next} construction permits handling of commands
%D that take arguments. This means that we can use this
%D command to redefine accent handling commands too.

\def\redefinecommand#1 %
  {\def\!!stringa{\nocharacterencoding#1}%
   \doifundefined{\!!stringa}
     {\@EA\letvalue\@EA\!!stringa\@EA=\csname#1\endcsname}%
   \setvalue{#1}{\dohandlecommand{#1}}}%

\unexpanded\def\dohandlecommand#1%
  {\doifdefinedelse{\characterencoding#1}
     {\def\next{\getvalue{\characterencoding#1}}}
     {\def\next{\getvalue{\nocharacterencoding#1}}}%
   \next}

%D \macros
%D   {redefinecharacter}
%D
%D Special characters, which differ from accented characters
%D in that they are to be presented as they are, are redefined
%D by
%D
%D \starttypen
%D \redefinecharacter  ae  % ae
%D \redefinecharacter  cc  % ccedilla
%D \stoptypen
%D
%D To keep things simple, we just copy this command:

\let\redefinecharacter=\redefinecommand

%D \macros
%D   {everyuppercase, EveryUppercase,
%D    everyuppercase, EveryUppercase}
%D
%D When we want to uppercase strings of characters, we have to
%D take care of those characters that have a special meaning or
%D are only accessible by means of macros. The next hack was
%D introduced when Tobias Burnus started translating head and
%D label texts into spanish and italian. The first application
%D of this token register therefore can be found in the module
%D that deals with these texts.

\newevery \everyuppercase \EveryUppercase
\newevery \everylowercase \EveryLowercase

%\appendtoks     \def\i{I}\to \everyuppercase
%\appendtoks     \def\j{J}\to \everyuppercase
%\appendtoks   \def\SS{SS}\to \everyuppercase % \SS <= \ss
%
%\appendtoks  \let\l=\L   \to \everyuppercase
%\appendtoks \let\ae=\AE  \to \everyuppercase
%\appendtoks \let\aa=\AA  \to \everyuppercase
%\appendtoks  \let\o=\O   \to \everyuppercase
%\appendtoks \let\oe=\OE  \to \everyuppercase

%D This magic trick maps takes care of mapping from lower to 
%D upper case and reverse. 

\appendtoks\let\setuppercasecom\setcasecom\to\everyuppercase
\appendtoks\let\setlowercasecom\setcasecom\to\everylowercase

\appendtoks\usemapping[\charactermapping]\to\everyuppercase
\appendtoks\usemapping[\charactermapping]\to\everylowercase

%D \macros
%D   {everysanitize, EverySanitize}
%D
%D Whenever we are sanitizing strings, like we sometimes do
%D when we deal with specials, the next token register can be
%D called.

\newevery \everysanitize \EverySanitize

%D \macros
%D   {obeylccodes}
%D
%D One way of manipulating characters is changing the their
%D \type{\lccode} and applying \type{\lowcase}. An example of
%D this can be found in \type{spec-mis}.

\def\obeylccodes%
  {\scratchcounter=32
   \loop
     \ifnum\scratchcounter<127
       \lccode\scratchcounter=\scratchcounter
       \advance\scratchcounter by 1
   \repeat
   \ifeightbitcharacters
     \scratchcounter=128
     \loop
       \ifnum\scratchcounter<255
         \lccode\scratchcounter=`.
         \advance\scratchcounter by 1
     \repeat
   \fi}

%D \macros
%D   {dotlessi,dotlessj}
%D
%D We also save both dotless~\dotlessi\ and~\dotlessj. This
%D way we still have them were we expect them, even when
%D macros of font providers redefine them.

\let\dotlessi=\i
\let\dotlessj=\j

%D Here come the definitions.

\redefineaccent    '   % grave
\redefineaccent    `   % acute
\redefineaccent    "   % dieresis
\redefineaccent    ^   % circumflex
\redefineaccent    ~   % tilde
\redefineaccent    v   % caron
\redefineaccent    u   % breve
\redefineaccent    .   % dotaccent
\redefineaccent    H   % hungarumlaut
\redefineaccent    t   % ........
\redefineaccent    r   % ........

\redefinecharacter ae  % ae
\redefinecharacter AE  % AE
\redefinecharacter oe  % oe
\redefinecharacter OE  % OE
\redefinecharacter o   % oslash
\redefinecharacter O   % Oslash
\redefinecharacter ss  % germandbls
\redefinecharacter SS  % germandbls
\redefinecharacter aa  % aring
\redefinecharacter AA  % Aring
\redefinecharacter cc  % ccedilla
\redefinecharacter CC  % Ccedilla

\redefinecommand b
\redefinecommand c
\redefinecommand d

\redefinecommand i % \definecharacter i "10
\redefinecommand j % \definecharacter j "11

\defineaccent " i {\"\i}  \defineaccent " j {\"\j}
\defineaccent ^ i {\^\i}  \defineaccent ^ j {\^\j}
\defineaccent ` i {\`\i}  \defineaccent ` j {\`\j}
\defineaccent ' i {\'\i}  \defineaccent ' j {\'\j}
\defineaccent ~ i {\~\i}  \defineaccent ~ j {\~\j}

%D Some more:

\startmapping[\nocharacterencoding] 

\defineuppercasecom \i  {I}
\defineuppercasecom \j  {J}
\defineuppercasecom \SS {SS}
\defineuppercasecom \l  \L 
\defineuppercasecom \ae \AE
\defineuppercasecom \aa \AA
\defineuppercasecom \o  \O 
\defineuppercasecom \oe \OE
\definelowercasecom \L  \l 
\definelowercasecom \AE \ae
\definelowercasecom \AA \aa
\definelowercasecom \O  \o 
\definelowercasecom \OE \oe

\stopmapping

%D We preload several encodings: 

\useencoding[ans,il2,pdf]

\protect 

\endinput 
