Token filter

Syntax

This callback is called whenever TeX needs a new token. No arguments are passed to the callback, and the return value should be either a Lua table representing a to-be-processed token, a table consisting of a list of such tokens, or something else like nil or an empty table. Since no argument is passed, if you want to get the next token in the document, you should use the token.get_next() function. Your lua function should therefore look like this:

function()
    return <table> token
end

If your Lua function does not return a table representing a valid token, it will be immediately called again, until it eventually does return a useful token or tokenlist (or until you reset the callback value to nil). If your function returns a single usable token, then that token will be processed by LuaTeX immediately. If the function returns a token list (a table consisting of a list of consecutive token tables), then that list will be pushed to the input stack at a completely new token list level. If what is passed to TeX is expandable, then the result of expansion is inserted into input and token.get_next() will grab it.

Examples

Faking \XeTeXinterchartoks

Note this is not strictly equivalent to the real XeTeX thing, because the latter operates on the character level. So, a\AA a, with \def\AA{A} doesn't work as expected.

Lua code:

% luatexinterchartoks.lua

charclasses = charclasses or {}

function setcharclass (a,b)
   charclasses[a] = b
end

local i = 0
while i < 65536 do
  charclasses[i]  = 0
  i = i + 1
end

interchartoks =  interchartoks or {}

function setinterchartoks (a,b,c)
   interchartoks[a] = interchartoks[a] or {}
   interchartoks[a][b] = c
end

local nc, oc
oc = 255

function do_intertoks () 
  local tok = token.get_next() 
  if tex.count['XeTeXinterchartokenstate'] == 1 then
      if tok[1] == 11 or  tok[1] == 12 then
        nc = charclasses[tok[2]] 
        newchar = tok[2]
      else 
        nc = 255
        newchar = ''
      end
      local insert  = ''
      if interchartoks[oc] and interchartoks[oc][nc] then
          insert = interchartoks[oc][nc] 
          local newtok = tok
          if insert<100 then
            local dec = math.floor(insert / 10) + 48;
            local unit = math.floor(insert % 10) + 48;
            newtok = {
              -- \XeTeXinterchartokenstate=0 \the\toks<n> \XeTeXinterchartokenstate=1
              token.create('XeTeXinterchartokenstate'),
              token.create(string.byte('='),12),
              token.create(string.byte('0'),12),
              token.create(string.byte(' '),10),
              token.create('the'),
              token.create('toks'),
              token.create(dec,12),
              token.create(unit,12),
              token.create(string.byte(' '),10),
              token.create('XeTeXinterchartokenstate'),
              token.create(string.byte('='),12),
              token.create(string.byte('1'),12),
              token.create(string.byte(' '),10),
              {tok[1], tok[2], tok[3]}}               
          end
          tok = newtok
      end
      oc = nc
  end
  return tok
end

callback.register ('token_filter', do_intertoks)

LaTeX package file:

% luatexinterchartoks.sty
\newcount\XeTeXinterchartokenstate

\newcount\charclasses
\def\newXeTeXintercharclass#1%
  {\global\advance\charclasses1\relax
   \newcount#1
   \global#1=\the\charclasses
   }

\newcount\cchone
\newcount\cchtwo

\def\dodoXeTeXcharclass
    {\directlua{setcharclass(\the\cchone,\the\cchtwo)}}

\def\doXeTeXcharclass%
   {\afterassignment\dodoXeTeXcharclass\cchtwo }

\def\XeTeXcharclass%
   {\afterassignment\doXeTeXcharclass\cchone }

\protected\def\XeTeXdointerchartoks%
   {\directlua{setinterchartoks(\the\cchone,\the\cchtwo,\the\allocationnumber)}}

\protected\def\dodoXeTeXinterchartoks%
   {\newtoks\mytoks\afterassignment\XeTeXdointerchartoks\global\mytoks }

\protected\def\doXeTeXinterchartoks%
   {\afterassignment\dodoXeTeXinterchartoks\cchtwo }

\def\XeTeXinterchartoks%
   {\afterassignment\doXeTeXinterchartoks\cchone }

\luatexdirectlua{require('luatexinterchartoks.lua')}

\endinput

Test document:

\documentclass{article}

\usepackage{luatexinterchartoks}
\usepackage{color}

\begin{document}

\newXeTeXintercharclass \mycharclassa
\newXeTeXintercharclass \mycharclassA
\newXeTeXintercharclass \mycharclassB
\XeTeXcharclass `\a \mycharclassa
\XeTeXcharclass `\A \mycharclassA
\XeTeXcharclass `\B \mycharclassB
% between "a" and "A":
\XeTeXinterchartoks \mycharclassa \mycharclassA = {[\itshape}
\XeTeXinterchartoks \mycharclassA \mycharclassa = {\upshape]}
% between " " and "B":
\XeTeXinterchartoks 255 \mycharclassB = {\bgroup\color{blue}}
\XeTeXinterchartoks \mycharclassB 255 = {\egroup}
% between "B" and "B":
\XeTeXinterchartoks \mycharclassB \mycharclassB = {.}

\begingroup
\XeTeXinterchartokenstate = 1
aAa A a B aBa BB
\endgroup

\end{document}