% -*- mode: Noweb; noweb-code-mode: icon-mode -*-
\documentclass{article}
\usepackage{noweb,multicol}

\title{Converting {\LaTeX} to HTML}
\author{Norman Ramsey\\{\tt nr@eecs.harvard.edu}}

\noweboptions{smallcode}
\setcounter{secnumdepth}{1}

\begin{document}
@
\pagenumbering{roman}
\maketitle
\tableofcontents
\pagenumbering{arabic}
@
\section{Introduction}
This program provides an infrastructure for converting {\LaTeX} to
HTML.
That infrastructure can be used to make a {\tt noweb} filter or to
make a standalone conversion program.
The program is roughly divided into three parts.
Section~\ref{cs-decls} assigns a meaning (treatment) to each control
sequence.
The first part is roughly declarative, and in principle it could be
 replaced by a data file.
The declarations can be  augmented dynamically by putting formal
comments in a {\LaTeX} or noweb file---the so-called
``nifty \verb+% l2h+ escape hatch,'' which is utterly necessary and utterly
undocumented. 
Section~\ref{engine} describes the engine used to do the conversion,
and
Sections \ref{imp-decl}~and~\ref{html-format} gives the procedures
that do the individual conversions. 

This program was motivated by my dissatisfaction with
\texttt{latex2html}.
In particular, \texttt{latex2html} is slow, and its output is full of
chartjunk.
Design decisions are driven by two goals:
\begin{itemize}
\item
Translate input eagerly as it is read in, in one pass whenever
possible.
For example, I take care to translate the body of [[\textbf{...}]]
without reading the entire argument.
Instead, I open the macro by emitting [[<b>]], and I note that a
corresponding [[</b>]] should be emitted when the matching close brace
is reached.
Most environments, including tables, are treated similarly.
The result is that \texttt{l2h} is \emph{fast}; it can comfortably
handle documents of hundreds of pages, whereas \texttt{latex2html}
starts bogging down at around 50~pages.%
\footnote{Measurement taken late in 1994}
\item
Use simple, natural translations to HTML whenever possible, and limit
functionality to simple translation.
For example, I do \emph{not} offer options to split documents up into
sections and to create hyperlinks between sections---that sort of
thing can and should be done by pure HTML tools.
Also, I make no real attempt to do anything fancy with equations or
pictures.
These things have no natural equivalents in HTML.
If you want to run {\LaTeX}, produce images, and embed them, look
elsewhere.
\end{itemize}
Finally, the program has to be able to translate a fragment at a time,
because it needs to work selectively on parts of the noweb pipeline.
For example, the argument to a {\LaTeX} control sequence might be
split into three pieces, one of which could be noweb quoted code.
Passing pieces in and getting results back incrementally
would be completely straightforward in a language with
message-passing concurrency, but we don't have that in Icon.
If I understood co-expressions, I might be able to use them, but
instead I use a continuation-passing, closure-passing style,
constantly creating actions to be executed on future input events.
Significant events include open and close braces as well as the simple
arrival of new text.
This style makes sense if one has some familiarity with continuations
\cite{appel:continuation,appel:compiling}, but for Icon programmers
it's bizarre.


{\bf Disclaimers}:  
This program may be the worst I have ever written.
It started as a weekend hack, then took on a life of its own.
As I gradually assimilated the weirdness of writing
continuation-passing code in Icon, I came up with better and better
ways of doing things, but all the old ways are still here.
I really ought to clean things up and document them, but that would
not help me get tenure.
Please excuse the weak or absent documentation.



@
\section{Descriptions of control sequences}
\label{cs-decls}

This section defines behavior for each control sequence we know how to
convert.
The definitions have a declarative flavor, since most are done by
procedure calls.
These calls initialize the machinery descriped in Section~\ref{cs-tables}.

{\LaTeX} control sequences come first, using
 the same organization as the quick reference card from the 
second edition of the {\LaTeX} manual.
Other control sequences follow.
@
\subsection{{\LaTeX} control sequences}
\subsubsection{Sentences and paragraphs}
<<control-sequence assignments>>=
substitution(",", " ")
substitution(" ", " ")
substitution("\n", "\n")
substitution("\t", " ")
ignore("raggedright")
ignore("@")
ignore("/")			# no italic correction
substitution("", "\n")		# \<newline> treated as request for newline
every c := !"$%#{}_" do
  substitution(c, c)
substitution("&", "&amp;")
argblock("emph", "em")
every argblock("footnote" | "footnotetext" | "thanks",
	       " <b>[</b>", "<b>]</b> ")   # put footnotes in bold brackets
substitution("today", &date)
@
\subsubsection{Type style}
<<control-sequence assignments>>=
ignore("textrm")		# html can't switch to default font!
argblock("textit", "i")     
argblock("textbf", "b")     
argblock("textsl", "i")     
ignore("textsc")
argblock("texttt", "tt")
ignore("textsf")
ignore("boldmath")
# \boldmath could be done by introducing S.mathfont, but I don't want to!
<<control-sequence assignments>>=
ignore("mathrm")		# html can't switch to default font!
argblock("mathit", "i")     
argblock("mathbf", "b")     
argblock("mathtt", "tt")
ignore("mathsf")
argblock("mathcal", "i")
every ignore("scriptstyle"|"displaystyle"|"scriptscriptstyle")
every ignore("mathord"|"mathbin"|"mathrel")
@ HTML has only one size.
<<control-sequence assignments>>=
every ignore("tiny" | "scriptsize" | "footnotesize" | "small" | "normalsize" | 
             "large" | "Large" | "LARGE" | "huge" | "Huge")
@
\subsubsection{Accents and symbols}
I've used a document from the W3~consortium to identify escapes for
symbols.
Older browsers won't support these symbols.
<<control-sequence assignments>>=
every accent(key(accent_name))
every ignore("dag" | "ddag")
substitution("S", "&sect;")
substitution("P", "&para;")
substitution("copyright", "&copy;")
substitution("pounds", "&pound;")
substitution("o", "&oslash;")
substitution("O", "&Oslash;")
substitution("aa", "&aring;")
substitution("AA", "&Aring;")
substitution("ae", "&aelig;")
substitution("AE", "&Aelig;")
@
\subsubsection{Sectioning and table of contents}
<<control-sequence assignments>>=
argblockv("part",          "h1", &null, "*[")
argblockv("chapter",       "h1", &null, "*[")
argblockv("section",       "h2", &null, "*[")     
argblockv("subsection",    "h3", &null, "*[")     
argblockv("subsubsection", "h4", &null, "*[")     
argblockv("paragraph",     "h5", &null, "*[")     
argblockv("subparagraph",  "h6", &null, "*[")     
ignore("appendix")
auxfile("tableofcontents", "toc", 
        "<p>\n<tableofcontents>\n<b>[Table of contents]</b>\n</tableofcontents>\n<p>", 
        "<h2>Table of Contents</h2>\n<tableofcontents>\n", "\n</tableofcontents>\n")
cstab["tableofcontents"] := Ctableofcontents # override to call set_toclevel
ignore("listoftables")
ignore("listoffigures")
ignore("addtocontents", "{{")
ignoreenv("filecontents", "{")
@
\subsubsection{Mathematical formulas}
Here we see our first assignments to [[cstab]], which is the real
technology underlying these seemingly declarative calls.
I'll assign to [[cstab]] directly when some really special behavior is
called for.  In this case, it's going in and out of math mode.
<<control-sequence assignments>>=
cstab["("] := Cmath
cstab[")"] := Cmath_end
cstab["["] := Cdisplaymath
cstab["]"] := Cdisplaymath_end
ignoreenv("equation")
every table_env(star("eqnarray"), 0, " ", "<blockquote><i>", "</i></blockquote>") 
							 # also lame
substitution("frac", "<b>frac</b>")
substitution("sqrt", "<b>frac</b>")
every substitution("ldots" | "cdots" | "vdots", "...")
ignore("left")
ignore("right")
ignore("overline")
substitution(":", " ")
substitution(";", " ")
ignore("!")
@ The [[star]] procedure lets us define \verb+eqnarray+ and
\verb+eqnarray*+ in one fell swoop.
<<*>>=
procedure star(cs)
  suspend cs | (cs || "*")
end
@
There are a gazillion symbols.  I'll add them on demand.
<<control-sequence assignments>>=
substitution("Diamond", "&lt;&gt;")
substitution("langle",  "&lt;")
substitution("rangle",  "&gt;")
substitution("le",      "&lt;=")
substitution("ne",      "!=")
substitution("ge",      "&gt;=")
substitution("times",   "&times;")
substitution("divide",  "&divide;")
substitution("bmod", "</i>mod<i>") # better hook in with math
substitution("equiv", "===")
every x := "arccos" | "arcsin" | "arctan" | "arg" | "cos" | "cosh" |
           "cot" | "coth" | "csc" | "deg" | "det" | "dim" | "exp" | 
           "gcd" | "hom" | "lim" | "liminf" | "limsup" | "ln" | "log" | 
           "max" | "min" | "sec" | "sin" | "sinh" | "sup" | "tan" | "tanh" 
do
  substitution(x, "</i>" || x || "<i>")
substitution("liminf", "</i>lim inf<i>")
substitution("limsup", "</i>lim sup<i>")
every x := "alpha" | "beta" | "gamma" | "delta" | "epsilon" | "zeta" | "eta" |
            "theta" | "iota" | "kappa" | "lambda" | "nu" | "xi" | "pi" | 
	    "rho" | "sigma" | "tau" | "upsilon" | "phi" | "chi" | "psi" | "omega" |
            "in"
do
  substitution(x, "<b>" || x || "</b>")
substitution("mu", "&micro;")
every x := "Gamma" | "Delta" | "Theta" | "Lambda" | "Xi" | "Pi" | "Sigma" |
            "Upsilon" | "Phi" | "Psi" | "Omega"
do
  substitution(x, "<b>" || x || "</b>")
@
Here are some lonesome math symbols.
<<control-sequence assignments>>=
substitution("lfloor", "</i>|_<i>")
substitution("rfloor", "</i>_|<i>")
substitution("leq", "&lt;=")
substitution("geq", "&gt;=")
substitution("ll", "&laquo;")
substitution("gg", "&raquo;")
substitution("Rightarrow", "==&gt;")
substitution("rightarrow", "--&gt;")
substitution("approx", "<u>~</u>")
@ 
\subsubsection{Displayed paragraphs}
HTML really has only one kind of displayed paragraph---the block quotation.
<<control-sequence assignments>>=
envblock("quote", "blockquote")
envblock("quotation", "blockquote")
envblock("center", "blockquote")
envblock("flushleft", "blockquote")
envblock("flushright", "blockquote")
envblock("verse", "blockquote")
verbatim("verbatim", escape_HTML_specials, "pre")
cstab["verb"] := Cverb
cstab["verb*"] := Cverb
csclosure["verb*"] := 1
cstab["verbatiminput"] := Cverbatiminput
csclosure["verbatiminput"] := verbatim_cl(escape_HTML_specials)
@ \verb*+\verb* uses visible blanks+. 
@
\subsubsection{Lists}
<<control-sequence assignments>>=
cstab["item"] := Citem
csclosure["item"] := [item_cl("<li>", "", "<li>")]
listenv("itemize", "ul")
listenv("enumerate", "ol")
listenv("description", "dl")
@
\subsubsection{Global or ignorable}
<<control-sequence assignments>>=
ignore("documentstyle", "[{")
ignore("documentclass", "[{")
ignore("usepackage", "[{")
ignore("pagestyle", "{")
ignore("thispagestyle", "{")
ignore("pagenumbering", "{")
ignore("newcounter", "{")
ignore("global")
ignore("etalchar") # used in the .bbl files: \newcommand{\etalchar}[1]{$^{#1}$}
@
\subsubsection{Title page and abstract}
I could be clever and have \verb+\title+ have a side effect
that sticks in the right boilerplate when we see \verb+\begin{document}+,
but for now it's not worth the hassle.
<<control-sequence assignments>>=
argblockv("title", "h1")
argblockv("author","address")
argblockv("date",  "b")
substitution("maketitle", "<!--title goes here-->")
ignoreenv("titlepage")
envblock("abstract", "<h2>Abstract</h2><blockquote>", "</blockquote>")
@
\subsubsection{Cross-reference}
A more ambitious scheme would make labels anchor at preceding
sectioning commands, but it's hard to see how to do that in one pass.
Instead, I just use some conventional glyphs.
I use special procedures for the cross-references so I can have an
arrow pointing either forward or backward, depending on the direction
of the reference.
<<control-sequence assignments>>=
cstab["label"] := Clabel
cstab["ref"] := Cref
cstab["pageref"] := Cref
cstab["subpageref"] := Cref
cstab["chunklabel"] := Clabel
@
\subsubsection{Bibliography and citation}
For the bibliography, I actually go grubbing for a {\tt .bbl} file if
I can find one.
<<control-sequence assignments>>=
ignore("bibliographystyle", "{")
auxfile("bibliography", "bbl", "<b>[BibTeX bibliography]</b>", &null, &null, "{")
envblock("thebibliography", "<h2>References</h2>", "", "{")
every cstab["cite" | "citeN" | "opencite" | "openciteN" | "citeyear"] := Ccite
cstab["bibitem"] := Cbibitem
ignore("newblock")
ignore("nocite", "{")
@
\subsubsection{Splitting the input}
All input is ignored.  Those things are in their own files.
<<control-sequence assignments>>=
every ignore("input" | "include" | "includeonly", "{")
# filecontents not done yet
@
\subsubsection{Line breaking}
<<control-sequence assignments>>=
cstab["\\"] := Cbackback
substitution("linebreak", "<br>")
ignore("-")
ignoreenv("sloppypar")
ignore("sloppy")
@
\subsubsection{Page breaking}
I simulate forced page breaks by horizontal rules.
<<control-sequence assignments>>=
substitution("pagebreak", "<hr>")
substitution("newpage", "<hr>")
substitution("clearpage", "<hr>")
ignore("enlargethispage", "*{")
@
\subsubsection{Boxes}
<<control-sequence assignments>>=
ignore("mbox")
ignore("makebox", "([[")  # ( comes from picture area
ignore("fbox")
ignore("framebox", "[[")  # could insert horizontal rules, but why?
ignore("newsavebox", 1)
ignore("sbox", 2)
ignore("savebox", "{[[{")
ignore("usebox", 1)
envblock("minipage", "blockquote", &null, "[{")
argblock("parbox",   "blockquote", &null, "[{")
@
\subsubsection{Space}
<<control-sequence assignments>>=
ignore("hspace", "*{")
ignore("hfil")
ignore("hfill")
ignore("vspace", "*{")
ignore("vfil")
ignore("vfill")
@
\subsubsection{Length}
<<control-sequence assignments>>=
ignore("newlength", "{")
ignore("setlength", "{{")
ignore("addtolength", "{{")
@
\subsubsection{Pictures}
<<control-sequence assignments>>=
envblock("picture", "<b>[picture]</b>", "", "((")
ignore("put", "({")
ignore("multiput", "(({{")
ignore("dashbox", "{([")
ignore("line", "({")
ignore("vector", "({")
ignore("shortstack", "[")
ignore("circle", "*{")
ignore("oval", "([")
ignore("frame")
ignore("thinlines")
ignore("thicklines")
@
\subsubsection{Figures and Tables}
I surround figures and tables with horizontal rules.
<<control-sequence assignments>>=
every envblock(star("figure"), "<hr>", "<hr>", "[")
every envblock(star("table"),  "<hr>", "<hr>", "[")
argblock("caption", "b")  # captions in bold
@
\subsubsection{{\tt tabbing} environment}
I can't see how to do anything sensible with {\tt tabbing}.
<<control-sequence assignments>>=
envblock("tabbing", "blockquote")
# \= is accent
ignore(">")
ignore("+")
ignore("kill")
@
\subsubsection{{\tt array} and {\tt tabular} environment}
<<control-sequence assignments>>=
tabular("array",    "[")
tabular("tabular",  "[")
tabular("tabularx", "{[")
tabular("tabular*", "{[")
every cstab["multicolumn"|"multispan"] := Cmulticolumn
cstab["span"] := Cspan
cstab["noalign"] := Cnoalign
cstab["hline"] := Chline
cstab["toprule"] := Chline
cstab["midrule"] := Chline
cstab["bottomrule"] := Chline
ignore("cline", "{")
ignore("newcolumntype", "{{")
@
\subsubsection{Definitions}
<<control-sequence assignments>>=
ignore("newcommand", "A[[{")
ignore("renewcommand", "A[[{")
ignore("providecommand", "A[[{")
ignore("newenvironment", "{[{{")
ignore("renewenvironment", "{[{{")
ignore("newtheorem", "{{")
@
\subsubsection{Numbering}
We have to have a special [[setcounter]] so we can ignore the right stuff
in the table of contents.
<<control-sequence assignments>>=
cstab["setcounter"] := Csetcounter
ignore("addtocounter", "{{")
@
\subsubsection{Other {\LaTeX} control sequences}
<<control-sequence assignments>>=
cstab["makeatletter"] := Cmakeatletter
cstab["makeatother"] := Cmakeatother
@
Here are all the old-style font changes.
<<control-sequence assignments>>=
every fontchange("tt" | "ttfamily", "tt")
every fontchange("bf" | "bfseries", "b")
every fontchange("it" | "itshape", "i")
fontchange("sl", "i")
fontchange("em", "em")
ignore("rm")		# html can't switch to default font!
ignore("sf")
ignore("sc")
@ And some new ones
<<control-sequence assignments>>=
ignore("rmfamily")
ignore("normalfont")
<<control-sequence assignments>>=
ignoreenv("document")
<<control-sequence assignments>>=
substitution("LaTeX", "LaTeX")
<<control-sequence assignments>>=
ignore("numberline", "{")
ignore("protect")
ignore("onecolumn")
ignore("twocolumn", "C")
ignore("typeout", "[{")
ignore("closedbib")
<<control-sequence assignments>>=
every ignore("leftmargini" | "leftmarginii" | "labelsep" | "fboxsep", "=")
every ignore("tabcolsep", "=")
every ignore("evensidemargin" | "marginparsep" | "marginparwidth" | 
             "oddsidemargin" | "textheight" | "textwidth" | "topmargin", "=")
<<control-sequence assignments>>=
ignore("DeclareMathVersion", "{")
ignore("mathversion", "{")
ignore("setpapersize", "{")
ignore("setmarginsrb", "{{{{{{{{")
ignore("marginparwidth", "=")
ignore("marginparsep", "=")
@
\subsection{Control sequences from various {\LaTeX} packages}
<<control-sequence assignments>>=
ignoreenv("multicols", "{C")
cstab["citeN"] := Ccite
ignore("afterpage", "{")
every cstab["psfig"|"epsfig"] := Cepsfig
cstab["includegraphics"] := Cincludegraphics
ignore("newcolumntype", "{{")
@
A (perhaps vain) attempt to implement \verb+\kill+.
<<control-sequence assignments>>=
cstab["kill"] := Ckill
@
\subsection{Plain {\TeX} control sequences}
<<control-sequence assignments>>=
activesubst("~", "&nbsp;")
argblock("centerline", "<br>", "<br>")
substitution("cr", "<br>")
substitution("hrule", "<hr>")
substitution("vrule", "|")
substitution("hrulefill", "------")
ignore("hyphenation", "{")
ignore("hbox")
ignore("rlap")
ignore("llap")
ignore("vbox")
ignore("vtop")
ignore("hidewidth")
ignore("message", "{")
ignore("relax")
ignore("null")
ignore("offinterlineskip")
ignore("omit")
ignore("newdimen", "{")
ignore("nobreak")
<<control-sequence assignments>>=
cstab["par"] := implicit_paragraph
cstab["smallskip"] := implicit_paragraph
cstab["medskip"] := implicit_paragraph
cstab["bigskip"] := implicit_paragraph
cstab["vskip"] := implicit_paragraph
csclosure["vskip"] := "="
@
We can't give the grouping control sequences their real meaning, because
that would blow our brace balance when ignoring definitions and the like.
The proper solution would be to distinguish between grouping and braces,
but that would require much more sophistication than we've got just now.
<<control-sequence assignments>>=
every ignore("begingroup" | "endgroup" | "bgroup" | "egroup")
<<control-sequence assignments>>=
cstab["newif"]   := Cnewif
cstab["iffalse"] := Ciffalse
cstab["iftrue"]  := Ciftrue
cstab["ifhtml"]  := Ciftrue  # false in LaTeX, but true when converting!
cstab["else"]    := Celse
cstab["fi"]      := Cfi
cstab["ifx"] := cstab["if"] := cstab["ifnum"] := Ciffalse
@ 
Lots of assignable things:
<<control-sequence assignments>>=
ignore("let", "A=")
every ignore("hfuzz" | "parindent" | "parskip" | "baselineskip", "=")
every ignore("hbadness" | "hsize" | "vsize" | "overfullrule" | "tabskip", "=")
every ignore("extrarowheight" | "codemargin", "=")
every ignore("looseness", "=")
substitution("hskip", " ", "=")
ignore("setbox", "{=")
every ignore("box" | "unhbox" | "unvbox", "{")
<<control-sequence assignments>>=
ignore("unskip")
ignore("hss")
ignore("phantom", "{")
every ignore("kern" | "lower" | "spacefactor", "=") # a cheat, but works
every ignore("clubpenalty" | "widowpenalty", "=")
@ 
Backslashes and delimiters.
<<new l2h.nw init declarative statements>>=
substitution("backslash", "\\")
ignore("delimiter", "=")
@
@ Other stuff to be ignored:
<<control-sequence assignments>>=
every ignore("expandafter" | "indent" | "noindent" | "leavevmode" | "strut")
ignore("def", 1)
<<control-sequence assignments>>=
substitution("TeX", "TeX")
substitution("BibTeX", "BibTeX")
substitution("MF", "METAFONT")
@ 
\subsubsection{HTML support for \TeX\ [[\char]]}

Process the numeric argument of a \TeX\ [[\char]] command that is of the form
`[[\char123]]' or `[[\char 123]]' (the [[\char]] has already been scanned, it
is no longer in the input)
and return the character with that code, which we hope will be ASCII
for reasonable implementations of Icon.
Also gobble any trailing whitespace.
<<control-sequence assignments>>=
cstab["char"] := asciiCharCode
<<*>>=
procedure asciiCharCode(S)
   return emit_text(S, char(2(optwhite(), TeXnumber(), optwhite())))
end
procedure TeXnumber()
  return integer(
    (="'",   "8r" || tab(many(&digits))) |
    (="\"", "16r" || tab(many(&digits))) |
    tab(many(&digits)))
end
@
\subsection{HTML support}
<<control-sequence assignments>>=
macro("nwanchorto",   2, "<a href=\"#$1\">#2</a>")
macro("nwanchorname", 2, "<a name=\"#$1\">#2</a>")
ignore("nwaddbox", "{")
verbatim("latexonly", do_nothing)
verbatim("rawhtml", emit_text)
@
\subsection{Other control sequences}
Here's some stuff that might be plain {\TeX}.
<<control-sequence assignments>>=
substitution("quad", " ")
@
I get to include my favorite {\TeX} hacks.
We define ignoring loosely; the count denotes the number of balanced-brace pairs.
We also ignore everything before an ignored balanced-brace pair, which means
it works for \verb+\def+.
<<control-sequence assignments>>=
ignore("noweboptions", 1)
@
Now, here are a couple of righteous hacks!
The idea is that most views will ignore this stuff, but the indexer might
use it to get clever about dumping chunks and all in the right places.
<<control-sequence assignments>>=
substitution("nowebindex", "<nowebindex>")
substitution("nowebchunks", "<nowebchunks>")
ignore("nowebsize")
<<control-sequence assignments>>=
envblock("fields",  "blockquote", &null, "[")     # lame; could try to <tt> 1st col
envblock("fields*", "blockquote", &null, "{")     # lame; could try to <tt> 1st col
ignore("citeauthoryear", "{{{")
ignore("authoryear", "{{")
substitution("bibrule", "--------")
let("bibskip", "par")
every cstab["anoncite"|"authorcite"] := Ccite
@
This will always have to be patched by hand, but it may be worth it.
<<control-sequence assignments>>=
ignore("pssilent")
ignore("psnoisy")
@


\section{The conversion engine}
\label{engine}

The converter doesn't have the luxury of working on the whole text at
once;  instead it has to accept and convert a piece at a time.
If I really understood co-expressions, I would surely make them sit up
and beg.
Since I don't, I keep some state around, and I pass continuations and
closures like there's no tomorrow.


@
\subsection{Basic conversion}
Here's the basic engine, which works by string scanning.
The initial boilerplate sets up the second argument (if any) as
[[&subject]].
The characters [[-]], [[']], and~[[`]] are special because they start
{\TeX} ligature.
We also have the odd specials [["\0"]] and [["\1"]], which are
used to delimit quoted code in noweb.
Woe betide the hapless user who has real nulls or 1s in his {\LaTeX} file.
<<*>>=
procedure convert(S, optstring)
  static specials
  initial { 
    <<initialization>>
    <<control-sequence assignments>>
    <<assign to dynamic-add table>>
    specials := '\\{}<>-\'`"%$&~\n\0\1' 
  }

  if \optstring then return optstring ? convert(S)
  else {
    <<scan, convert, and return result>>
  }
end
@
If I were a good dog, I would make a state diagram.
Since I'm not, I'll just say that we either
accumulate text using the function [[S.text]], which exists for that
purpose, or else we do something special upon encountering a special character.

The [[<<take actions appropriate to new text>>]] 
chunk may do something special with the text in
case we're not in the default state (for example, we may be scanning
for the end of a comment).

Encountering a non-threatening character throws the converter into
horizontal mode.
<<scan, convert, and return result>>=
<<take actions appropriate to new text>>
if S.mode == "V" & any(~'\\{}<>%\n\t ') then S.mode := "H"
emit_text(S, tab(upto(specials) | 0))
while not pos(0) do 
  if S.mode == "Q" then { # quoting
    emit_text(S, tab(upto('\1') | 0))
    if ="\1" then {
      emit_text(S, "\1")
      S.mode := S.quotemode
    }
  } else {
    if any(S.activechars) then
      do_activechar(S, move(1))
    else
      case move(1) of {
        "\\" : {<<control sequence>>}
        "{"  : {<<take open-group actions>>}
        "}"  : {<<take close-group actions>>}
        "%"  : {<<comment>>}
        "\n" : {<<newline>>}
        "$"  : {<<dollar sign>>}
        "&"  : ampersand(S)
        "\0" : {S.quotemode := S.mode; S.mode := "Q"; emit_text(S, "\0")}
        # remaining cases simply escape HTML specials
        "<"  : emit_text(S, "&lt;")
        ">"  : emit_text(S, "&gt;")
        "\"" : emit_text(S, "&quot;")
        "-"  : {<<deal with dash ligatures>>}
        "`"  : {<<deal with open quotes>>}
        "'"  : {<<deal with close quotes>>}
      }
    if S.mode == "V" & any(~'\\{}<>%\n\t ') then S.mode := "H"
    emit_text(S, tab(upto(specials++S.activechars) | 0))
  }
return 1(. S.the_text, S.the_text := "")  # what's been converted
<<deal with dash ligatures>>=
if S.mode == "V" then S.mode := "H"
if S.mode == "H" then
    if ="--" then emit_text(S, "&mdash;")
    else if ="-" then emit_text(S, "&ndash;")
    else emit_text(S, "-")
else
    emit_text(S, "-")
@ 
<<*>>=
global html_quotes # render quotes as HTML 4 entities
<<deal with open quotes>>=
if S.mode == "V" then S.mode := "H"
if \html_quotes & S.mode == "H" then
    if ="`" then emit_text(S, "&ldquo;")
    else emit_text(S, "&lsquo;")
else
    emit_text(S, "`")
<<deal with close quotes>>=
if S.mode == "V" then S.mode := "H"
if \html_quotes & S.mode == "H" & ="'" then emit_text(S, "&rdquo;")
else                                        emit_text(S, "'")
@
The definition of a converter's state is distributed.
We've already seen the use of [[mode]].
<<*>>=
record state(mode, quotemode <<other fields of state>>)
	# mode is Q, H, V, or M
	# quotemode is saved mode: H, V, or M
@
To create a new state, the default mode is vertical
<<*>>=
procedure converter(mode)
  /mode := "V"
  return state(mode, mode <<initial values for other fields of state>>)
end
@
To avoid repeated memory allocation, we provide a routine to reset a
converter to its initial state.
<<*>>=
procedure reset(S)
  <<code to reset [[S]]>>
  return S
end
@
The basic action performed by the
[[S.text]] function is to accumulate converted text in [[S.the_text]].
[[S.text]] is usually [[accumulate_text]].
<<*>>=
procedure accumulate_text(S, text)
  S.the_text ||:= text
  return
end
<<other fields of state>>=
, text, the_text
<<initial values for other fields of state>>=
, accumulate_text, ""
<<code to reset [[S]]>>=
S.text := accumulate_text
S.the_text := ""
@
[[emit_text]] just uses the current value of [[S.text]], provided we aren't
currently ignoring tokens.
Its primary use is to appear in closures, when we don't know what
[[S.text]] will be when the closure is executed.
<<*>>=
procedure emit_text(S, text)
  return if \S.ignoring then "" else S.text(S, text)
end
<<other fields of state>>=
, ignoring
<<initial values for other fields of state>>=
, &null
<<code to reset [[S]]>>=
S.ignoring := &null
@ 
Active characters are like control sequences.
The only one active by default is the~[[~]].
<<*>>=
global activetab, activeclosure
procedure do_activechar(S, c)
  (activetab[c])(S, c, activeclosure[c])
  return
end
<<initialization>>=
activetab := table(unknown_cs)
activeclosure := table()
<<other fields of state>>=
, activechars
<<initial values for other fields of state>>=
, '~'
<<code to reset [[S]]>>=
S.activechars := '~'
@
\subsection{Action and continuation hooks}
We provide hooks so that actions can be taken at various points.
The major ones are:
\begin{description}
\item[\tt newtext]
When the next string is passed in for conversion.
\item[open brace]
After the next open brace or begin environment.
\item[close brace]
Before the next close brace or end environment.
\end{description}
@
\subsubsection{{\tt newtext}}
[[newtext]] is a list of closures to be executed (actions to take)
 when the next input comes.
<<other fields of state>>=
, newtext
<<initial values for other fields of state>>=
, []
<<code to reset [[S]]>>=
S.newtext := []
@
A closure is simply a procedure with arguments.
<<*>>=
record closure(proc, args)
@
[[before_next_newtext]] and [[after_next_newtext]] 
add to the list of actions to be taken (at the left and right, respectively).
<<*>>=
procedure before_next_newtext(S, proc, args)
  push(S.newtext, closure(proc, args))
end

procedure after_next_newtext(S, proc, args)
  put(S.newtext, closure(proc, args))
end
@
When taking the actions, be careful to avoid infinite loop, e.g., on empty lines.
<<take actions appropriate to new text>>=
l := S.newtext
S.newtext := []
while c := get(l) do
  c.proc!c.args
@
Some control sequences temporarily override all actions to be taken on
a new input, using [[delay_newtext]].
 [[undelay_newtext]] restores actions.
<<*>>=
procedure delay_newtext(S)
  push(S.delayed_newtext, S.newtext)
  S.newtext := []
  return
end

procedure undelay_newtext(S)
  S.newtext := \pop(S.delayed_newtext) |
    {write(&errout, "This can't happen: no delayed_newtext"); &null[0]}
end
<<other fields of state>>=
, delayed_newtext
<<initial values for other fields of state>>=
, []
<<code to reset [[S]]>>=
S.delayed_newtext := []
@
\subsubsection{Opening and closing groups}
There's only one list of actions to be taken at the next open,
but there's a whole stack of lists of actions to be taken at closes.
<<other fields of state>>=
, open, closes
<<initial values for other fields of state>>=
, [], []
<<code to reset [[S]]>>=
every S.open | S.closes := []
<<*>>=
procedure after_next_open(S, proc, args)
  return put(S.open, closure(proc, args))
end

procedure before_next_close(S, proc, args)
  return push(S.closes[1], closure(proc, args)) # lost at top level
end

procedure after_next_close(S, proc, args)
  return put(S.closes[1], closure(proc, args)) # lost at top level
end
<<take open-group actions>>=
push(S.closes, []) # fresh set of closing tasks
while c := get(S.open) do
  c.proc!c.args
<<take close-group actions>>=
while c := get(S.closes[1]) do
  c.proc!c.args
pop(S.closes)
<<old>>=
procedure Cbegingroup(S, cs, cl)
 <<take open-group actions>>
end
<<old>>=
procedure Cendgroup(S, cs, cl)
 <<take close-group actions>>
end
<<old control-sequence assignments>>=
cstab["begingroup"] := Cbegingroup
cstab["endgroup"]   := Cendgroup
cstab["bgroup"]     := Cbegingroup
cstab["egroup"]     := Cendgroup
@
\subsection{Handling control sequences and environments}
OK, to eat a control sequence, first scan it, then execute it using [[do_cs]].
[[S.csletters]] records the current set of ``letters'' for control
sequences (so we can interpret \verb+\makeatletter+).
<<control sequence>>=
cs := if pos(0) then ""
      else if any(S.csletters) then tab(many(S.csletters))
      else move(1)
if /S.ignoring | cs == ("else"|"fi") | cstab[cs] === (Ciffalse|Ciftrue) then
  do_cs(S, cs)
else
  &null # error("### Ignoring \\", cs)
<<other fields of state>>=
, csletters
<<initial values for other fields of state>>=
, &letters
<<code to reset [[S]]>>=
S.csletters := &letters
@
To execute a control sequence, look up its procedure in [[cstab]],
and pass in the name of the control sequence, plus the closure
argument from [[csclosure]].
\label{cs-tables}
<<*>>=
global cstab, csclosure

procedure do_cs(S, cs)
  tab(many(' \t')) # skip white space following CS
  if pos(0) | any('\n') then before_next_newtext(S, skipblanks, [S])
  (cstab[cs])(S, cs, csclosure[cs])
  return 
end
<<initialization>>=
cstab := table(unknown_cs)
csclosure := table()
@
The default action for an unknown control sequence is [[unknown_cs]].
If the global [[show_unknowns]] is set we dump the control sequence into the 
output in bold.  We save the unknown sequences for later warning messages.
<<*>>=
global show_unknowns
procedure unknown_cs(S, cs, cl)
#  if S.text === ignore_text then return # a bit of a hack  -- should no longer be needed
  if \show_unknowns then S.text(S, "<b>\\" || cs || "</b>")
  if not member(unknown_set, cs) then {
    write(\unknown_file, "Warning: unknown control sequence \\", cs)
    insert(unknown_set, cs)
  }
  return
end
<<initialization>>=
unknown_set := set()
<<*>>=
global cstab, csclosure, unknown_set
@
The control sequences \verb+\begin+ and \verb+\end+ are treated
specially,
so we can have a similar machinery for environments.
<<*>>=
global begintab, endtab, begincl, endcl

procedure do_begin(S, cs, cl)
  (="{", env := tab(upto('}')), ="}") | error("botched \\begin{...}")
  <<take open-group actions>>
  (begintab[env])(S, env, begincl[env])
  return 
end

procedure do_end(S, cs, cl)
  (="{", env := tab(upto('}')), ="}") | error("botched \\end{...}")
  # write(&errout, "calling ", image(endtab[env]), " for \\end{", env, "}")
  (endtab[env])(S, env, endcl[env])
  <<take close-group actions>>
  return 
end
<<control-sequence assignments>>=
cstab["begin"] := do_begin
cstab["end"]   := do_end
<<initialization>>=
every begintab | endtab := table(unknown_env)
every begincl  | endcl  := table()
<<*>>=
procedure unknown_env(S, env, cl)
###  if S.text === ignore_text then return # a bit of a hack # no longer needed
  if \show_unknowns then S.text(S, "<b>{" || env || "}</b>")
  if not member(unknown_envs, env) then {
    write(\unknown_file, "Warning: unknown environment {", env, "}")
    insert(unknown_envs, env)
  }
  return
end
<<initialization>>=
unknown_envs := set()
<<*>>=
global unknown_envs
@
\subsection{Issuing warnings about unknown control sequences and environments}
<<*>>=
procedure warn_unknown(s, type, mark, rmark)
  if *s > 0 then {
    pushout("Unknown " || type || ": ")
    every pushout(((\mark | "")\1) || !sort(s) || ((\rmark | "")\1) || " ")
    pushout("\n")
 }
end
<<*>>=
procedure pushout(s)
  static col
  initial col := 0
  if find("\n", s) then
    s ? {
      pushout(tab(upto('\n')))
      while ="\n" do {col := 0; write(&errout)}
      pushout(tab(0))
    }  
  else {
    col +:= *s
    if col >= 79 then {writes(&errout, "\n  "); col := *s + 2}
    writes(&errout, s)
  }
  return
end
@
\subsection{Procedures related to parsing {\TeX}}
\subsubsection{Comment-skipping}
This logic gobbles text into [[S.comment]]
until a newline is encountered, at which point it calls 
[[Ccomment]] to format the comment.
All other new-text actions go on hold until the comment is over.
<<comment>>=
parse_dynamic_add(S)
delay_newtext(S)
eat_comment(S)
<<*>>=
procedure eat_comment(S)
  S.comment ||:= tab(upto('\n') | 0)
  if pos(0) then
    before_next_newtext(S, eat_comment, [S])
  else {
    undelay_newtext(S)
    Ccomment(S)
    S.comment := ""
  }
  return
end    
<<other fields of state>>=
, comment
<<initial values for other fields of state>>=
, ""
<<code to reset [[S]]>>=
S.comment := ""
@
Verbatim text is a little bit like comment text---we keep swallowing
under special rules until we find a terminator.
There are at least three classes of rules:
\begin{itemize}
\item
Copy text, but escape the HTML specials.
This corresponds to an ordinary {\LaTeX} \texttt{verbatim}
environment.
\item
Copy text while changing nothing.
This correspondes to a \texttt{rawhtml} environment.
\item
Throw everything on the floor.
This corresponds to a \texttt{latexonly} environment.
\end{itemize}
We store an output method, a string that terminates the environment,
and possibly  tag for an HTML wrapper around the environment.
<<*>>=
record verbatim_cl(output, terminator, html, translate_blank)

procedure verbatim(name, output, html)
  begintab[name] := Cverbatim
  begincl [name] := verbatim_cl(output, &null, html)
  return
end

procedure Cverbatim(S, cs, cl)
  if cl === begincl[cs] & /cl.terminator then
    cl := begincl[cs] :=
      verbatim_cl(cl.output, "\\end{" || cs || "}", cl.html, cl.translate_blank)
  emit_text(S, tag(\cl.html))
  delay_newtext(S)
  do_verbatim(S, cl)
  return
end
@
If we find the terminator, we're finished.
Otherwise, we swallow the whole input and make sure our action on next
input is to continue scanning.
<<*>>=
procedure do_verbatim(S, cl)
  if cl.output(S, tab(find(cl.terminator)), cl) then {
    =cl.terminator
    emit_text(S, endtag(\cl.html))
    undelay_newtext(S)
  } else {
     cl.output(S, tab(0), cl)
     before_next_newtext(S, do_verbatim, [S, cl])
  }
  return
end
@
When writing verbatim text, we still have to convert HTML specials.
<<*>>=
procedure escape_HTML_specials(S, s, cl)
  s ? {
    while emit_text(S, tab(upto('&<>" '))) do
      case move(1) of {
        "\"" : emit_text(S, "&quot;")
        "&"  : emit_text(S, "&amp;")
        "<"  : emit_text(S, "&lt;")
        ">"  : emit_text(S, "&gt;")
        " "  : emit_text(S, if \cl.translate_blank then "&middot;" else " ")
      }
    emit_text(S, tab(0))
  }
  return
end
@
The \verb+\verb+ control sequence's terminator is the first character
following \verb+\verb+.
<<*>>=
procedure Cverb(S, cs, cl)
  Cverbatim(S, cs, verbatim_cl(escape_HTML_specials, move(1), "tt", cl))
  return
end
@ 
<<*>>=
procedure Cverbatiminput(S, cs, cl)
  local filename, f, line
  if ="{" & filename := tab(upto('}')) & ="}" then {
    f := \open(filename) | { emit_text(S, "<strong>Could not read file</strong> <tt>")
                             escape_HTML_specials(S, filename, cl)
                             emit_text(S, "</tt>")
                             return
                           }
    emit_text(S, "\n<pre>\n")
    while line := read(f) do {
      escape_HTML_specials(S, line, cl)
      emit_text(S, "\n")
    }
    emit_text(S, "</pre>\n")
    close(f)
  }
  return
end
@
\subsubsection{Arguments}
It's occasionally necessary to collect the argument of a control
sequence.
[[csarg]] does the job.
<<*>>=
procedure csarg(S)
  return  2(="{", tab(bal('}', '{', '}')), ="}") |
           (optwhite(), 
               if ="\\" then 
                 "\\" || (tab(many(S.csletters)) | move(1))
               else
                 move(1))
end
@ 
[[csarg()]] works only if the whole
argument is in the same line; otherwise it only returns the opening curly
brace, `[[{]]'. Another problem with [[csarg()]] is that it does not cope with 
[[%]] or [[\]] in the input (due to the use of the Icon function [[bal()]] to 
balance curly brackets), as such a escaped or commented out curly brace is 
handled incorrectly.

The solution provided here is not trivial. The problem is that if we have
`[[\foo{bar]]' in a line and the `[[baz}]]' is in another line then due to the
way how l2h works the Icon command associated with [[foo]] will have to 
terminate before the `[[baz}]]' gets read, and as such cannot do anything 
useful except register a callback to finish the job.

@

[[apply_arg(S, cl)]] scans an argument (preceded by optional
whitespace), then invokes the closure on that argument.
Its use should subsume [[csarg]], but that may take a while yet.
<<*>>=
@ 
[[apply_args(S, p, as, n]] scans [[n]] arguments from the
input, puts them in a list [[args]], then calls [[p!(as ||| args)]].
This is a bit weak, because we really want to turn off comment
skipping for some arguments.
N.B. the arguments are \emph{not} converted.
<<*>>=
procedure apply_args(S, p, as, args_wanted)
  delay_newtext(S)
  do_apply_args(S, closure(p, as), args_wanted, [], "", 0)
  return
end

procedure do_apply_args(S, cl, wanted_count, args_seen, current_arg, brace_depth)
  local open_comment
  # invariant : we have an open brace
#  pushtrace("APPLY")
  while *args_seen < wanted_count & not pos(0) do {
    while *args_seen < wanted_count & brace_depth = 0 & not pos(0) do {
      tab(many(' \t\n'))
      case c := move(1) of {
        "\\" : put(args_seen, "\\" ||
                 if pos(0) then ""
                 else if any(S.csletters) then tab(many(S.csletters))
                 else move(1))
        "{"  :  { current_arg := "" ; brace_depth := 1 }
        "}"  :  { error("Insufficient arguments to macro ", macro.name) }
        "%"  :  if tab(upto('\n')) then ="\n" else open_comment := tab(0)
        default : put(args_seen, c)
      }
    }
    while brace_depth > 0 & not pos(0) do {
      current_arg ||:= tab(upto('\\{}%') | 0)
      case move(1) of {
        "%"  :  if tab(upto('\n')) then ="\n" else open_comment := tab(0)
        "\\" : current_arg ||:= "\\" ||
                 if pos(0) then ""
                 else if any(S.csletters) then tab(many(S.csletters))
                 else move(1)
        "{"  :  { current_arg ||:= "{" ; brace_depth +:= 1 }
        "}"  :  { brace_depth -:= 1
		  if brace_depth > 0 then
		    current_arg ||:= "}"
		  else {
		    put(args_seen, current_arg)
		    current_arg := ""
		  }
		}
      }
    }
  }
  if *args_seen = wanted_count then {
    undelay_newtext(S)
    cl.proc ! (cl.args ||| args_seen)
  } else if \open_comment then {
    delay_newtext(S)
    before_next_newtext(S, skip_comment_and_continue,
	[S, closure(do_apply_args, [S, cl, wanted_count, args_seen,
				    current_arg, brace_depth])])
  } else
    before_next_newtext(S, do_apply_args, [S, cl, wanted_count, args_seen,
					   current_arg, brace_depth])
#  poptrace()
  return
end
<<*>>=
procedure skip_comment_and_continue(S, cl)
  tab(upto('\n') | 0)
  if pos(0) then
    before_next_newtext(S, skip_comment_and_continue, [S, cl])
  else {
    ="\n"
    undelay_newtext(S)
#    <take actions appropriate to new text>>
  }
  return
end    
@
\subsubsection{Misc specials}
Ampersands are covered in the table section (\ref{tabular}).
@
The dollar sign is for entering and exiting math mode:
<<dollar sign>>=
if /S.ignoring then
  if ="$" then
    if S.mode == "M" then { Cdisplaymath_end(S); S.mode := "V" }
    else                  { Cdisplaymath(S);     S.mode := "M" } 
  else
    if S.mode == "M" then { Cmath_end(S); S.mode := "H" }
    else                  { Cmath(S);     S.mode := "M" } 
@
Newlines emit themselves, plus start skipping blanks until they get to
some nonblank text.
We have to identify a blank line so we can insert a paragraph marker.
<<newline>>=
emit_text(S, "\n")
if /S.ignoring then Cnewline(S)
<<*>>=
procedure Cnewline(S)
  tab(many(' \t'))
  if match("\n") then implicit_paragraph(S)
  if pos(0) then before_next_newtext(S, Cnewline, [S])
end
@
Other procedures might want to skip white space, which includes
newlines, but we don't want to miss a paragraph.
<<*>>=
procedure skipblanks(S)
  tab(many(' \t'))
  if ="\n" then Cnewline(S)
  else if pos(0) then before_next_newtext(S, skipblanks, [S])
end
@
Paragraphs count only in horizontal or math mode (and they better not
happen in math mode!).
<<*>>=
procedure implicit_paragraph(S, cs, cl)
  if S.mode ~== "V" then {
    S.mode := "V"
    Cparagraph(S)
  }
  cs_ignore(S, cs, \cl)
end
@
Here's a real hack.  I use it to stop skipping blanks when the noweb
filter sees text quoted by [[[[...]]]].
That text is never converted, but we don't want to skip blanks that
follow it.
<<*>>=
procedure stop_skipping(S)
  while S.newtext[1].proc === (Cnewline|skipblanks) do pop(S.newtext)
end
@
\subsubsection{Items}
For items, we actually want to do something with the optional arguments,
namely, convert them.
We wrap them in braces so that any font changes and so on will be 
appropriately limited in their effects.
<<*>>=
record item_cl(before, after, ifnone)

procedure Citem(S, cs, cl)
  if pos(0) then 
    after_next_newtext(S, Citem, [S, cs, cl])
  else if ="[" then {
    delay_newtext(S)
    with_upto_bracket(S, "", convert_bracketed, cl)
  } else {
    skipblanks(S)
    emit_text(S, cl[1].ifnone)
    \liststack[1] := \liststack[1] + 1
  }
end
<<*>>=
procedure convert_bracketed(S, contents, cl)
  emit_text(S, cl[1].before || 
            convert(converter("H"), "{" || contents || "}") || 
            cl[1].after)
  optwhite()
end
<<*>>=
global liststack, suspendstack
<<initialization>>=
liststack := []
# write(&errout, "Initialized liststack")
suspendstack := []
<<control-sequence assignments>>=
cstab["suspend"] := Csuspend
cstab["resume"] := Cresume
<<*>>=
procedure listenv(env, html)
  begintab[env] := Clist
  begincl[env] := html
  endtab[env] := Clist_end
  endcl[env] := html
end
  
procedure push_item_closure(cs)
  push(csclosure["item"], 
    if cs == "description" then item_cl("<dt>", "<dd>", "<dt><dd>")
    else                        item_cl("<li>", "--", "<li>"))
end

procedure Clist(S, cs, cl)
  push(liststack, 1)
  push_item_closure(cs)
  emit_text(S, tag(cl))
end

procedure Cresume(S, cs, cl)
  local n, env
  (="{", env := tab(upto('}')), ="}") | error("botched \\resume{...}")
  n := pop(suspendstack) | error("\\resume not balanced by corresponding \\suspend")
  push(liststack, n)
  push_item_closure(env)
  if env == "enumerate" then
    emit_text(S, tag(begincl[env] || " start=\"" || n || "\""))
  else
    emit_text(S, tag(begincl[env]))
end

procedure Clist_end(S, cs, cl)
  emit_text(S, endtag(cl))
  pop(csclosure["item"])
  pop(liststack)
end

procedure Csuspend(S, cs, cl)
  local env
  (="{", env := tab(upto('}')), ="}") | error("botched \\suspend{...}")
  emit_text(S, endtag(endcl[env]))
  pop(csclosure["item"])
  push(suspendstack, pop(liststack))
end
@
\subsubsection{Labels and references}
These could be done by [[argblock]], except I want to make it possible to have
different text depending on whether the references point forward or backward.
<<*>>=
global labels_seen

procedure Clabel(S, cs, cl)
  initial /labels_seen := set()
  insert(labels_seen, l := csarg(S)) | fail
  emit_text(S, "<a name=\"" || l || "\"><b>[*]</b></a>")
end

procedure Cref(S, cs, cl)
  local prefix, prefix_tag
  initial /labels_seen := set()
  prefix_tag := (\cl)[1] | ""
  prefix := (\cl)[2] | ""
  l := prefix || csarg(S) | fail
  emit_text(S, prefix_tag || "<a href=\"#" || l || "\">[" || 
                 (if member(labels_seen, l) then "&lt;-" else "-&gt;") || "]</a>")
end
@
\subsubsection{Citations}
The important thing about a citation key is that it makes a hot line
to the appropriate item in the bibliography.
[[Ccite]] and [[Cbibitem]] work together to make it happen.

Optional arg might contain blanks, so it might be split, but
 I assume the citation key isn't split between inputs.
<<*>>=
procedure Ccite(S, cs, cl, bracketed_text)
  if ="[" then {
    delay_newtext(S)
    with_upto_bracket(S, "", do_cite, cl)
  } else
    do_cite(S, &null, cl)
end

procedure do_cite(S, commentary, cl)
  local key
  if \commentary then
    optwhite()
  if pos(0) then before_next_newtext(S, do_cite, [S, commentary, cl])
  else {
    key := csarg(S)
    \commentary := convert(converter("H"), "{" || \commentary || "}")
    emit_text(S, "<b>[cite&nbsp;")
    key ? {
      while k := tab(upto(",")) & ="," do
        emit_text(S, "<a href=\"#NWcite-" || k || "\">" || k || "</a>, ")
      if k := tab(0) then
        emit_text(S, "<a href=\"#NWcite-" || k || "\">" || k || "</a>")
    }
    emit_text(S, ", <i>" || \commentary || "</i>")
    emit_text(S, "]</b>")
  }
end
<<*>>=
procedure Cbibitem(S, cs, cl)
  local label, key
  static counter
  initial counter := 0
  if ="[" then {
    delay_newtext(S)
    with_upto_bracket(S, "", finish_bibitem, [])
  } else {
    label := "<b>[" || (counter +:= 1) || "]</b>"
    apply_args(S, do_bibitem_key, [S, label], 1)
  }
end

procedure do_bibitem_key(S, label, key)
  return emit_text(S, "<a name=\"NWcite-" || key || "\">" || label || "</a> ")
end

procedure finish_bibitem(S, contents, args)
  local key, label
  optwhite()
  label := convert(converter("H"), "{" || contents || "}")
  key := apply_args(S, do_bibitem_key, [S, label], 1)
end
@
\subsubsection{Conditionals}
The idea here is that an \verb+\if+$\cdots$ control sequence will conditionally 
ignore text, and that \verb+\fi+ restores the previous state.
To keep track of state, we have an ``if stack'' that records what
[[S.text]] should be upon encountering \verb+\else+ and \verb+\fi+.
<<other fields of state>>=
, ifstack
<<initial values for other fields of state>>=
, []
<<code to reset [[S]]>>=
if *S.ifstack > 0 then S.ifstack := []  # keeps GC down
@
What's on the ifstack is
<<*>>=
record ifrec(on_else, on_fi)
@ It's possible that one day this code will need to be updated to delay
new-text actions (and to do God knows what if
new-text actions have already been delayed).
@
Every \verb+\if+$\cdots$ is equivalent either to \verb+\iffalse+
of \verb+\iftrue+, so we begin by defining those, as well as \verb+\else+
and \verb+\fi+
<<*>>=
procedure Ciffalse(S, cs, cl)
#error("### \\", cs, " -> false (S.ignoring === ", image(S.ignoring) ? {="procedure "; tab(0)}, ")")
  push(S.ifstack, ifrec(S.ignoring, S.ignoring))
  S.ignoring := 1
end

procedure Ciftrue(S, cs, cl)
#error("### \\", cs, " -> true (S.ignoring === ", image(S.ignoring) ? {="procedure "; tab(0)}, ")")
  push(S.ifstack, ifrec(1, S.ignoring))
end

procedure Celse(S, cs, cl)
  S.ignoring := S.ifstack[1].on_else
#error("### \\else -> S.ignoring === ", image(S.ignoring) ? {="procedure "; tab(0)})
end

procedure Cfi(S, cs, cl)
  S.ignoring := S.ifstack[1].on_fi
#error("### \\fi -> S.ignoring === ", image(S.ignoring) ? {="procedure "; tab(0)})
  pop(S.ifstack)
end
@
Now, all that's left is to handle \verb+\newif+.
This part is all boilerplate.
<<*>>=
procedure Cnewif(S, cs, cl)
  local newif, newcs
  tab(many(' \t\n'))
  if pos(0) then
    after_next_newtext(S, Cnewif, [S, cs, cl])
  else {
    newif := csarg(S)
    newif ?
      if ="\\if" & newcs := tab(many(S.csletters)) & pos(0) then {
        <<make [[newcs]] a new \verb+\if+-like thing>>
      } else
        error("\\newif argument botch: " || newif)
  }
end
@
And here we do the real work:
<<make [[newcs]] a new \verb+\if+-like thing>>=
cstab[newcs || "false"] := Csetif
cstab[newcs || "true"]  := Csetif
cstab["if" || newcs] := Ciffalse
<<*>>=
procedure Csetif(S, cs, cl)
  local base, tag
  if cs ? (base := tab(find("true"|"false")), tag := =("true"|"false"), pos(0)) then {
    cstab["if" || base] := if tag == "true" then Ciftrue else Ciffalse
  } else {
    error("This can't happen --- setif botch (not urgent)")
  }
end
@ 
\subsection{Upper case}

This is a very simple implementation of [[\uppercase]]: it requires to
have all of its argument immediately.
<<*>>=
procedure Cuppercase(S, cs, cl)
  l := map(csarg(S), &lcase, &ucase) | fail
  emit_text(S, l)
end
<<control-sequence assignments>>=
cstab["uppercase"] := Cuppercase
@ 
\subsection{HTML support for array and tabular environments}
We handle tables by using [[S.text]] to implement a little state machine.
There are only two states: waiting to start a new cell, and the
ordinary state of converting text.

The rest of the state information is held in a list of [[table_info]]
records that tell us what to expect for the next cell.
<<*>>=
record table_info(index,	# number of this cell in the row
		  alignment,	# the alignment of this cell 
		  width,	# how many columns this cell will span
		  alignments,	# default alignments for this table
		  brace_depth,	# size of S.closes after start of cell
		  cell_text)	# value of S.text to use to scan this cell
@ This state could conceivably be extended to include pre- and
post-content for each cell, \`a la plain {\TeX}'s [[\halign]] or the
{\LaTeX} [[<{}]] and [[>{}]] directives, but for now I won't bother.

I should probably also add a [[rows_taken]] field and use it to
implement [[multirow]] support.
@
Here's a stack that keeps track of all currently active tabular environments.
<<other fields of state>>=
, tables
<<initial values for other fields of state>>=
, []
<<code to reset [[S]]>>=
S.tables := []
@ 
Accumulating text forces the transition between states.
While I'm at it, I update the state for the next cell.
<<*>>=
procedure start_table_cell(S, text)
  local this, attributes

  text ? {
    tab(many(' \t\n'))
    if pos(0) then return
  }
# write(&errout, "starting cell with ", image(text))

  this := S.tables[1] | fatal("starting cell with no current table")
  S.text := this.cell_text

if /(\this).brace_depth then write(&errout, "starting table cell, ", image(this), " has null brace depth")
  # use this to start the current cell
  if this.index = 1 then emit_text(S, "<tr>")
  attributes := \this.alignment | aligneq("top")
  if this.width > 1 then attributes ||:= " colspan=" || this.width
  emit_text(S, "<td" || attributes || ">")

  # now update state for the next cell
  this.index +:= this.width  # advance to next cell
  this.alignment := this.alignments[this.index] | &null
  this.width := 1
  # can't set cell_text until we hit &

  <<take open-group actions>>
  emit_text(S, text)
  return
end
@ 
Hitting an ampersand closes and opens groups, and it advances to the
next cell.
<<*>>=
procedure ampersand(S)
  local this
  this := S.tables[1]
  <<take close-group actions>>
  if /this then
    emit_text(S, " --- ")
  else {
    emit_text(S, "")  # be sure cell gets started, even if empty
    emit_text(S, "</td>")
    if S.text ~=== start_table_cell then
       this.cell_text := S.text
    S.text := start_table_cell
    this.brace_depth := *S.closes + 1 # will open at start of cell
#write(&errout, "set brace depth for ", image(this))
  }
  tab(many(' \t\n'))
##  write(&errout, " past &, text = ", image(S.text), ", next = ",
##  	 image(&subject[&pos:0]))
  return
end
@
The double backslash is the end of a row, unless it's buried in braces
or there's no table.
We have to be careful about ignoring a square bracket, because if the
[[\\]] is at the end of a line, we won't know until we see the newline
that it's not a bracket, and we don't see the newline until we get the
next text.
We therefore must use a continuation-passing style for this ignore.
<<*>>=
procedure Cbackback(S, cs, cl)
  local this
  this := S.tables[1]
  cs_ignore(S, cs, "[", Cbackback_continue, [S, this])
end

procedure Cbackback_continue(S, this)
#if /(\this).brace_depth then write(&errout, image(this), " has null brace depth")
  if /this | *S.closes > this.brace_depth then { # ordinary \\
    S.text(S, "<br>")
  } else {			# row terminator
## write(&errout, "ending row with ", image(&subject[&pos:0]))
    emit_text(S, "")  # be sure cell gets started, even if empty
    <<take close-group actions>>
    emit_text(S, "</td></tr>\n")
    tab(many(' \t\n'))
    if S.text ~=== start_table_cell then
      this.cell_text := S.text
    this.index := 1
    this.alignment := this.alignments[this.index] | &null
    this.width := 1
    S.text := start_table_cell
    this.brace_depth := *S.closes + 1 # about to open
  }
end
@
A horizontal line disappears if it's in a table.
<<*>>=
procedure Chline(S, cs, cl)
  if \S.tables[1] then return
  else emit_text(S, "<hr>")
  return
end
@ 
An [[\end{tabular}]] terminates the whole affair.
If we're at the beginning of a row, things are easy.
Otherwise, we terminate the current row first.
<<*>>=
procedure Ctabular_end(S, cs, cl)
  local this
  if S.text ~=== start_table_cell | S.tables[1].index > 1 then {# row in progress
    emit_text(S, "")  # be sure cell gets started, even if empty
    <<take close-group actions>>
    emit_text(S, "</td></tr>")
  }
  if S.text === start_table_cell then # abort it
    S.text := S.tables[1].cell_text
  emit_text(S, "</table>")
  xxx := pop(S.tables)
#write(&errout, "popped ", image(xxx))
  return
end
@ 
Finally, the setup of the table itself:
<<*>>=    
procedure Ctabular(S, cs, cl)
  cs_ignore(S, cs, cl, Ctabular_continue, [S])
  return
end

procedure Ctabular_continue(S)
  a := csarg() # alignment
#write(&errout, "Alignment ", a)
  emit_text(S, if upto('|', a) then "<table border>" else "<table>")
  emit_text(S, "<!-- alignment is " || a || "-->")
  a := alignments(a)
  emit_text(S, "<!-- " || *a || " columns-->")
  push(S.tables, table_info(1, a[1] | "l", 1, a, *S.closes+1, S.text))
#write(&errout, "pushed ", image(S.tables[1]))
  S.text := start_table_cell
  optwhite()
  return
end
@ Earlier, the initial value of [[S.tables[1].brace_depth]] was
[[&null]], but when we had alignment of \verb+{c}+, it was never
getting set, so I'm setting it on startup, even though I'm not sure if
that's really right.
<<*>>=
procedure tabular(env, ignore)
  begintab[env] := Ctabular
  begincl[env] := ignore
  endtab[env] := Ctabular_end
  endcl[env] := ignore
end
@ 
We figure alignments using the tricks in the {\LaTeX} book.
<<*>>=
procedure aligneq(a)
  return " align=\"" || a || "\""
end

procedure valigneq(a)
  return " valign=\"" || a || "\""
end

procedure alignments(s)
  a := []
  s ? {
    while not pos(0) do
      case move(1) of {
	"l" | "X" | "Y" | "p" :
            { put(a, aligneq("left") || valigneq("top")); skip_bracket() }
	"c" : put(a, aligneq("center"))
	"r" : put(a, aligneq("right"))
	"m" : { put(a, aligneq("left") || valigneq("center")); skip_bracket() }
	"b" : { put(a, aligneq("left") || valigneq("bottom")); skip_bracket() }
	"@" | "<" | ">" | "!" : skip_bracket()
        "|" : &null
        default : &null		# unrecognized...
      }
  }
  return a
end
<<*>>=
procedure skip_bracket()
  if ="{" then {
    n := 1
    while n > 0 & not pos(0) do {
      tab(upto('{}\\') | 0)
      case move(1) of {
        "{" : n +:= 1
	"}" : n -:= 1
	"\\" : move(1)
      }
    }
  }
  return
end
@ 
[[\multicolumn]] changes the width and alignment of the current cell.
[[\multispan]] changes only the width.
<<*>>=
procedure Cmulticolumn(S, cs, cl)
  local this
  this := S.tables[1]
  n := integer(csarg()) | error("\\multicolumn or \\multispan not followed by integer")
  if cs == "multicolumn" then a := alignments(csarg())
# write(&errout, "\\", cs, "  n = ", n, ",  a = ", (\a)[1] | "???", 
#      ", text = ", image(S.text))
  if /this then return		# \multicolumn without table?
  this.width := n
  this.alignment := (\a)[1]
  return
end

procedure Cspan(S, cs, cl)
  (\S.tables[1]).width +:= 1
  return
end
@ 
<<*>>=
procedure Cnoalign(S, cs, cl)
  apply_args(S, finish_noalign, [S], 1)
  return
end

procedure finish_noalign(S, arg)
  return if \S.ignoring then "" else 
  accumulate_text(S, "<br>" || convert(converter("V"), "{" || arg || "}") || "<br>")
end
@ 
\subsection{Reading and converting auxiliary {\LaTeX} files}
<<*>>=
procedure auxfile(cs, ext, placeholder, header, trailer, ignore)
  cstab[cs] := Cauxfile
  csclosure[cs] := aux_cl(ext, placeholder, header, trailer, \ignore | "")
end
@
[[Cauxfile]] succeeds if it finds a file, fails otherwise.
<<*>>=
record aux_cl(ext, placeholder, header, trailer, ignore)

procedure Cauxfile(S, cs, cl)
  local auxfile, T
  if auxfile := open(basename(\curfile) || "." || cl.ext) then {
    T := converter("V")
    Cmakeatletter(T)
    S.text(S, \cl.header)
    while line := read(auxfile) do 
      S.text(S, convert(T, line || "\n"))
    close(auxfile)
    S.text(S, \cl.trailer)
  } else {
    S.text(S, \cl.placeholder)
  }
  cs_ignore(S, cs, cl.ignore)
  if \auxfile then return
end
<<*>>=
procedure basename(name)
  reverse(name) ? {
    tab(upto('.')) & ="."
    return reverse(tab(0))
  }
end
@
\subsubsection{Table of contents}
We can build a table of contents by reading the .toc file.
Sadly, I haven't figured out how to get hot links yet.
<<control-sequence assignments>>=
cstab["contentsline"] := Ccontentsline
<<*>>=
procedure Ctableofcontents(S, cs, cl)
  S.mode := "V"
  Cauxfile(S, cs, cl)
  set_toclevel(S)
end
@
[[set_toclevel]] manages the starting and ending of lists.
With no level argument, it resets the toc to the initial level.
<<*>>=
procedure set_toclevel(S, l)
  static toclevel, initiallevel
  if /initiallevel := \l then
    S.text(S, "<ul compact>")
  if /l := \initiallevel then
    S.text(S, "</ul>")
  if /l then return  # never set a level
  /toclevel := l
  while toclevel < l do {
    S.text(S, "<ul compact>")
    toclevel +:= 1
  }
  while toclevel > l do {
    S.text(S, "</ul>")
    toclevel -:= 1
  }
  return
end
@
Assume one table of contents per converted document.
<<*>>=
procedure Ccontentsline(S, cs, cl) 
  local type, level
  static leveltab
  initial { <<assign numbers of sections in leveltab>> }
  l := \leveltab[csarg()] | fail
  if l > \countertab["tocdepth"] then
    cs_ignore(S, cs, "{{") # skip this one
  else {
    set_toclevel(S, l)
    S.text(S, "<li>")
    after_next_open(S, after_next_close, [S, cs_ignore, [S, cs, "{"]])
  }
end
<<assign numbers of sections in leveltab>>=
l := ["part", "chapter", "section", "subsection", "subsubsection", 
      "paragraph", "subparagraph"]
leveltab := table()
every i := 1 to *l do
  leveltab[l[i]] := i - 2  # making section level 1
@
\subsubsection{Counters}
<<*>>=
global countertab

procedure Csetcounter(S, cs, cl)
  local counter
  (counter := csarg(), countertab[counter] := integer(csarg())) | 
	cs_ignore(S, cs, "{{")
end
<<initialization>>=
countertab := table()
@
\subsubsection{Accents}
This info is taken from the HTML RFC, section entitled 
``ISO Latin~1 character entities.''
<<*>>=
global accent_name, accent_valid
<<initialization>>=
accent_name  := table()
accent_valid := table('')
accent_name ["`"]  := "grave"
accent_valid["`"]  := 'AEIOUaeiou'
accent_name ["'"]  := "acute"
accent_valid["'"]  := 'AEIOUYaeiouy'
accent_name ["^"]  := "circ"
accent_valid["^"]  := 'AEIOUaeiou'
accent_name ["hat"]  := "circ"
accent_valid["hat"]  := 'AEIOUaeiou'
accent_name ["\""] := "uml"
accent_valid["\""] := 'AEIOUaeiouy'
accent_name ["~"]  := "tilde"
accent_valid["~"]  := 'ANOano'
accent_name ["="]  := "bar"
accent_name ["."]  := "dot"
accent_name ["u"]  := "u"
accent_name ["v"]  := "v"
accent_name ["H"]  := "H"
accent_name ["t"]  := "t"
accent_name ["c"]  := "cedil"
accent_valid["c"]  := 'Cc'
accent_name ["d"]  := "underdot"
accent_name ["b"]  := "underbar"
@
Initialization calls [[accent]] to indicate that a control
sequence represents an accent.
In fact, [[accent]] is called on all keys of [[accent_name]].
<<*>>=
procedure accent(cs)
  cstab[cs] := Caccent
end

procedure Caccent(S, cs, cl)
  static warned
  initial warned := table()
  arg := csarg(S) | return
  if arg == "\\i" then arg := "i"
  if arg == "\\j" then arg := "j"
  if *arg = 1 & any(accent_valid[cs], arg) then
    S.text(S, "&" || arg || accent_name[cs] || ";")
  else {
    <<warn about [[cs]] with [[arg]]>>
    S.text(S, arg)
  }
end
<<warn about [[cs]] with [[arg]]>>=
/warned[cs] := set()
if not member(warned[cs], arg) then {
  write(&errout, "Warning: Can't handle \\", cs, " with arg `", arg, "'")
  insert(warned[cs], arg)
}
@
\subsection{Font changes}
A font change changes the font until the next close, when we need to emit
the appropriate end tag.
<<*>>=
procedure fontchange(tex, html)
  cstab[tex] := Cfontchange
  csclosure[tex] := html
end
<<*>>=
procedure Cfontchange(S, tex, html)
  S.text(S, tag(html))
  before_next_close(S, emit_text, [S, endtag(html)])
end
@
\section{Implementations of declaratives}
\label{imp-decl}

\subsection{Ignoring stuff}
There are several different kinds of things that can be ignored:
ordinary arguments,
balanced-brace arguments, optional arguments, assignments (which may
include dimensions), stars, and parenthesized coordinates.
We ignore a sequence of these things by supplying a template to
[[ignore]], in which each character stands for something to be ignored.
We've already seen examples of these things in Section~\ref{cs-decls}.

We can ignore arguments of control sequences or environments.
In either case, [[cs_ignore]] does the work.
<<*>>=
procedure ignore(cs, template)
  /template := ""
  cstab[cs] := cs_ignore
  csclosure[cs] := template
end

procedure ignoreenv(env, template)
  /template := ""
  begintab[env] := cs_ignore
  begincl[env] := template
  endtab[env] := do_nothing
end
@
Because ignoring may span many inputs, all [[cs_ignore]] does is set things
up to call [[do_ignore]].  
The major setup is replacing [[S.text]] with a function that does nothing.
Oh, and it converts an integer template
into that many arguments, for historical reasons.
<<*>>=
procedure cs_ignore(S, cs, template, proc, args)
  local saved_ignore
  saved_ignore := S.ignoring
  S.ignoring := 1
  if type(template) == "integer" then template := repl("{", template)
  return do_ignore(S, template, saved_ignore, proc, args)
end
@
Some things are easily ignored (partly because we assume they don't
span inputs).  For others, we have special procedures.
The brace-ignoring stuff uses the open and close hooks, because braces
can be nested deeply.
If non-null, [[proc]] is applied to [[args]] after everything is ignored.
<<*>>=
procedure do_ignore(S, template, saved_ignore, proc, args)
  if *template > 0 then
    if optwhite() & pos(0) then
      after_next_newtext(S, do_ignore, [S, template, saved_ignore, proc, args])
    else
      case template[1] of {
        "{" : { S.ignoring := 1
                after_next_open(S, ignore_til_close, 
			              [S, template[2:0], saved_ignore, proc, args])
              }
        "A" : { csarg(S) # had better be in one input
                do_ignore(S, template[2:0], saved_ignore, proc, args)
              }
        "[" : if optwhite() & ="[" then {
                delay_newtext(S)
		with_upto_bracket(S, "", ignore_bracket_plus,
  		                            [S, template[2:0], saved_ignore, proc, args])
              } else
                do_ignore(S, template[2:0], saved_ignore, proc, args)
        "C" : # a total cheat, means ``copy optional arg''
              if optwhite() & ="[" then {
                S.ignoring := &null
                delay_newtext(S)
		with_upto_bracket(S, "", copy_bracket_plus,
  		                            [S, template[2:0], saved_ignore, proc, args])
              } else
                do_ignore(S, template[2:0], saved_ignore, proc, args)
        "=" : { delay_newtext(S)
                eat_assignment(S, do_ignore, [S, template[2:0], saved_ignore, proc,args])
              }
        "*" : { (="*", optwhite())
                do_ignore(S, template[2:0], saved_ignore, proc, args)
              }
        "(" : { (="(", tab(upto(')')), =")", optwhite())
                do_ignore(S, template[2:0], saved_ignore, proc, args)
              }
      }
  else {
    S.ignoring := saved_ignore
    (\proc)!(\args)
  }
end

procedure ignore_til_close(S, template, saved_ignore, proc, args)
  before_next_close(S, do_ignore, [S, template, saved_ignore, proc, args])
end
@
Finally, at the end of an ignored environment, do nothing.
<<*>>=
procedure do_nothing(S, cs, cl)
  return
end
@
\subsubsection{Parsing bracketed (optional) arguments}
We may have to deal with optional arguments that are split across lines.
We pass in a continuation for the bracket.
This is a lot like gobbling to a newline, which we had to do with a comment.
As in the other case, we do something stupid if the bracket is
protected (e.g. by a backslash or comment char).
<<*>>=
procedure with_upto_bracket(S, bracketed_text, proc, args)
  bracketed_text ||:= tab(upto(']') | 0)
  if pos(0) then
    before_next_newtext(S, with_upto_bracket, [S, bracketed_text, proc, args])
  else {
    ="]"
    undelay_newtext(S)
    (\proc)(S, bracketed_text, args)
  }
  return
end    
@
To ignore brackets:
<<*>>=
procedure ignore_bracket_plus(S, contents, args)
  # contents are ignored
  do_ignore!args
end
@ and to copy them
<<*>>=
procedure copy_bracket_plus(S, contents, args)
  local should_ignore
  should_ignore := args[3] | fail  # saved_ignore arg to do_ignore
  if /should_ignore then
    S.text(S, convert(converter("H"), "{" || contents || "}"))
  do_ignore!args
end
@
\subsubsection{Ignoring assignments}
Assignments are tricky because they might involve numbers, control
sequences, dimensions, or even glue.
We approximate the syntax from page 275 in the \TeX book.
<<*>>=
procedure eat_assignment(S, proc, args)
  static decimal_chars, hex_chars, oct_chars
  initial {
    decimal_chars := &digits ++ '.,+-'
    hex_chars := &digits ++ 'abcdefABCDEF'
    oct_chars := '0124567'
  }
  optwhite()
  ="="		# so what if we swallow multiple = signs
  optwhite()
  if pos(0) then {
    before_next_newtext(S, eat_assignment, [S, proc, args])
    return
  } else if glue() then { # finished
  } else if any(decimal_chars) then {
    tab(many(decimal_chars))
    optwhite()
    if ="\\" then
      tab(many(S.csletters)) | move(1)
    # else assume assignment of the form \hangafter=2
  } else if ="\"" then {
    tab(many(hex_chars)) & optwhite()
  } else if ="\'" then {
    tab(many(oct_chars)) & optwhite()
  } else if =("\\"|"`\\") then
    tab(many(S.csletters)) | move(1)
  undelay_newtext(S)
  (\proc)!args
end
<<*>>=
procedure dimen()
  static decimal_chars
  initial decimal_chars := &digits ++ '.,'
  suspend (optwhite(), 
           if any('+-') then (move(1), optwhite()) else "",
           tab(many(decimal_chars)), optwhite(), 
           (="true", optwhite()) | &null,
           =("em"|"ex"|"pt"|"pc"|"in"|"bp"|"cm"|"mm"|"dd"|"cc"|"sp"|"mu"))
end
<<*>>=
procedure glue() 
  suspend (dimen(), 
           (optwhite(), ="plus",  dimen()) | "", 
           (optwhite(), ="minus", dimen()) | "")
end
@
\subsection{Substitution}

\subsubsection{Simple substitution for a single control sequence}

Even simple substitution isn't so simple, because in addition to the
HTML that we substitute for the {\TeX}, we can also supply a template
of stuff to be ignored (like the optional argument to \verb+\\+).
<<*>>=
procedure substitution(tex, html, ignore_template)
  # ignore mode for now
  cstab[tex] := Cemit_ig
  csclosure[tex] := emit_ig_cl(html, \ignore_template | "")
end
@
The closure contains HTML to be written and a template to be ignored.
<<*>>=
record emit_ig_cl(html, template)

procedure Cemit_ig(S, cs, cl)
  emit_text(S, cl.html)
  if *cl.template > 0 then 
    cs_ignore(S, cs, cl.template)
end
@ 
\subsubsection{Substitution for active characters}
<<*>>=
procedure activesubst(char, html, ignore_template)
  local S
  # ignore mode for now
  activetab[char] := Cemit_ig
  activeclosure[char] := emit_ig_cl(html, \ignore_template | "")
  S := \dynamic_add_hack | return
  if upto(S.activechars, char) then return # already active
  if S.activechars ++:= cset(char) then {
    before_next_close(S, delete_active_char, [S, char])
  } else impossible("ugh")
  return
end

procedure delete_active_char(S, char)
  S.activechars --:= char
  return
end
@
\subsubsection{Substitution for environments}
The [[envblock]] procedure has two forms:
\begin{itemize}
\item
{}[[envblock(]]{\it environment}, {\it tag}[[)]] simply uses
begin- and end-{\it tag} in place of the environment.
\item
{}[[envblock(]]{\it environment}, {\it left}, {\it right}, {\it
ignore}[[)]] 
puts the {\it left} text at the beginning of the environment, the {\it
right} text at the end, plus at the beginning of the environment it
ignores the arguments described by {\it ignore}.
\end{itemize}
It's easier to implement than to describe.
<<*>>=
procedure envblock(env, left, right, ignore_template)
  /ignore_template := ""
  begintab[env] := Cemit_ig
  begincl[env] := emit_ig_cl(if /right then tag(left) else left, ignore_template)
  endtab[env] := Cemit
  endcl[env] := if /right then endtag(left) else right
end
@ [[Cemit]] emits text with nothing to ignore.
<<*>>=
procedure Cemit(S, cs, cl)
  S.text(S, cl)
end
@
\subsubsection{Substitution around arguments of control sequences}
These substitutions place tags at the beginning and end of arguments
to control sequences, instead of surrounding the contents of an
environment.
For example, they specify how to convert [[\section{...}]] to
[[<h1>...</h1>]] and so forth.
The calling convention is as for [[envblock]].
<<*>>=
record blockpair(left, right, ignore)

procedure argblock(tex, html, right, ignore)
  # called as is envblock
  /ignore := ""
  cstab[tex] := Cblock
  csclosure[tex] := 
    if /right then blockpair (tag(html),  endtag(html), ignore)
    else blockpair (html, right, ignore)
end
@ There is a fine point; control sequences labelled with [[argblockv]]
should put the converter into vertical mode.
<<*>>=
procedure argblockv(tex, html, right, ignore)
  argblock(tex, html, right, ignore)
  cstab[tex] := CblockV
end
<<*>>=
procedure Cblock(S, cs, cl, done_ignoring)
  if /done_ignoring & *cl.ignore > 0 then {
    cs_ignore(S, cs, cl.ignore, Cblock, [S, cs, cl, 1])
  } else if pos(0) then {
    after_next_newtext(S, do_cs, [S, cs, cl])
  } else if match("{") then {
    S.text(S, cl.left)
    after_next_open(S, before_next_close, [S, emit_text, [S, cl.right]])
  } else {
#    S.text(S, cl.left || csarg(S) || cl.right)
    apply_args(S, Cblock_continue, [S, cl], 1)
  }
  return
end

procedure Cblock_continue(S, cl, title)
  S.text (S, cl.left || title || cl.right)
  return
end
<<*>>=
procedure CblockV(S, cs, cl)
  S.mode := "V"
  Cblock(S, cs, cl)
  return
end
@
\subsubsection{Macro substitution}
I'm taking the plunge and describing a ghastly macro language.
Macros have arguments, a body, and an optional terminal mode.
The final mode, if non-null, is the mode to which the conversion
engine should be set.
<<*>>=
record macro_defn(name, arg_count, body, mode)
@ The body is a list of items, where an item may be a raw argument, a
converted argument, or a string.
<<*>>=
record raw_arg(number)
record converted_arg(number, mode)
@ 
<<*>>=
procedure expand_macro(S, macro, args)
  every a := !macro.body do 
    case type(a) of {
      "string"  : emit_text(S, a)
      "raw_arg" : emit_text(S, args[a.number]) | impossible("missing arg")
      "converted_arg" : S.text(S, convert(S, "{" || args[a.number] || "}"))
    }
#  poptrace()
  return
end
#link pushtrace
@ 
Scan arguments and hope comments in arguments just work out.  Ha ha.
<<*>>=
procedure do_macro(S, macro, args_seen, current_arg, brace_depth)
  # invariant : we have an open brace
#  write(&errout, "scanning args for macro ", macro.name)  
#  write(&errout, "seen ", *args_seen, " want ", macro.arg_count)  
  while *args_seen < macro.arg_count & not pos(0) do {
    while *args_seen < macro.arg_count & brace_depth = 0 & not pos(0) do {
#  write(&errout, "seen ", *args_seen, " want ", macro.arg_count,
#	 " current ", image(current_arg), " braces ", brace_depth)  
      tab(many(' \t\n'))
      case c := move(1) of {
        "\\" : put(args_seen, "\\" ||
                 if pos(0) then ""
                 else if any(S.csletters) then tab(many(S.csletters))
                 else move(1))
        "{"  :  { current_arg := "" ; brace_depth := 1 }
        "}"  :  { error("Insufficient arguments to macro ", macro.name) }
        default : put(args_seen, c)
      }
    }
    while brace_depth > 0 & not pos(0) do {
#  write(&errout, "seen ", *args_seen, " want ", macro.arg_count,
#	 " current ", image(current_arg), " braces ", brace_depth)  
      current_arg ||:= tab(upto('\\{}') | 0)
      case move(1) of {
        "\\" : current_arg ||:= "\\" ||
                 if pos(0) then ""
                 else if any(S.csletters) then tab(many(S.csletters))
                 else move(1)
        "{"  :  { current_arg ||:= "{" ; brace_depth +:= 1 }
        "}"  :  { brace_depth -:= 1
		  if brace_depth > 0 then
		    current_arg ||:= "}"
		  else {
		    put(args_seen, current_arg)
		    current_arg := ""
		  }
		}
      }
    }
  }
#  write(&errout, "seen ", *args_seen, " want ", macro.arg_count,
#	 " current ", image(current_arg), " braces ", brace_depth)  
  if *args_seen = macro.arg_count then {
#    write(&errout, "Arguments for macro ", macro.name, ":")
#    every write(&errout, "\t", image(!args_seen))
    expand_macro(S, macro, args_seen)
    undelay_newtext(S)
  } else
    before_next_newtext(S, do_macro, [S, macro, args_seen, current_arg, brace_depth])
  return
end
@ 
<<*>>=
procedure Cmacro(S, cs, cl)
#  pushtrace("MACRO")
  delay_newtext(S)
#   apply_args(S, closure(expand_macro, [cl]), cl.arg_count)
  do_macro(S, cl, [], "", 0)
  return
end
@ 
Now, a {\TeX}-like macro facility in which [[#]] is used for converted
parameters and [[#$]] for raw ones.
<<*>>=
procedure macro(name, arg_count, body, mode)
  m := macro_defn(name, arg_count, parse_body(body), mode)
  cstab[name] := Cmacro
  csclosure[name] := m
  return
end      

procedure begin_macro(env, arg_count, body, mode)
  m := macro_defn(env, arg_count, parse_body(body), mode)
  begintab[env] := Cmacro
  begincl[env] := m
  return
end      

procedure parse_body(body)
  b := []
  body ? {
    put(b, tab(upto('#') | 0))
    while ="#" do {
      put(b, ="#" | (="$", raw_arg(argnum())) | converted_arg(argnum())) |
	                                    error("malformed macro arg #", tab(0))
      put(b, tab(upto('#') | 0))
    }
  }
  return b
end

procedure argnum()
  if any(&digits) then return integer(move(1)) else fail
end
@ 
And the dynamic version\ldots
<<*>>=
procedure l2h_macro(name, count, body[])
  count := integer(count) |
      return error("must give # of arguments to l2h macro ", name)
  s := ""
  every s ||:= " " || (1(b := !body, type(b) == "string"))
  s := s[2:0] # strip leading space if any
  return macro(name, count, s)
end
@ 
<<*>>=
procedure l2h_environment(env, count, body[])
  count := integer(count) |
      return error("must give # of arguments to l2h environment ", env)
  s := ""
  every s ||:= " " || (1(b := !body, type(b) == "string"))
  s := s[2:0] # strip leading space if any
  return begin_macro(env, count, s)
end
@
\subsection{Table environments}
For tables, we not only have an HTML tag, we also supply some text
for the ampersand.
[[args]] is a template describing the arguments to the environment,
which are ignored.
<<*>>=
record table_closure(args, amp, open, close)

procedure table_env(env, args, amp, open, close)
  begintab[env] := Ctable
  begincl[env] := table_closure(args, amp, 
                                      if /close then tag(\open)    | &null else open,
                                      if /close then endtag(\open) | &null else close)
  endtab[env] := Ctable_end
  endcl[env] := []
end
<<*>>=
procedure Ctable(S, env, cl)
  local amp
##  amp := S.ampersand
##  S.ampersand := cl.amp
  S.text(S, \cl.open)
  push(endcl[env], amp)
  cs_ignore(S, env, cl.args)
end

procedure Ctable_end(S, env, cl)
#  S.ampersand := pop(cl)
  S.text(S, \begincl[env].close)
end
@ 
\subsection{Postscript}
<<*>>=
procedure Cepsfig(S, cs, cl)
  apply_args(S, do_epsfig, [S], 1)
end

procedure do_epsfig(S, arg) 
  local args 
  args := []
  arg ? 
    while not pos(0) do {
      tab(many(' \t\n'))
      put(args, eqsplit(tab(upto(',') | 0)))
    }
  if a := !args & a.name == ("file"|"figure") then
    emit_text(S, "<a href=" || image(a.value) || "><b>[</b>PostScript figure " ||
	          a.value || "<b>]</b></a>")
  else
    emit_text(S, "<b>[</b>Ill-understood PostScript figure<b>]</b>")
end

record apair(name, value)

procedure eqsplit(s)
  p := apair()
  s ? (p.name := tab(upto('=')), ="=", p.value := tab(0))
  return p
end
@ 
<<*>>=
procedure Cincludegraphics(S, cs, cl)
  local saved_ignore
  saved_ignore := S.ignoring
  S.ignoring := 1
  do_ignore(S, "[", saved_ignore, apply_args, [S, do_includegraphics, [S], 1])
end

procedure do_includegraphics(S, arg) 
  local base, ext
  if arg ? (base := tab(find(ext := ".ps" | ".eps" | ".epsi")), =ext, pos(0)) then
    emit_text(S, "<a href=" || image(arg) || "><b>[</b>PostScript figure " ||
	          arg || "<b>]</b></a>")
  else if arg ? (base := tab(find(ext := ".png" | ".gif" | ".jpg")), =ext, pos(0)) then
    emit_text(S, "<img src=" || image(arg) || ">")
  else
    emit_text(S, "<b>[</b>Ill-understood graphics<b>]</b>")
end
@
\subsection{Control-sequence assignment}
This procedure is available to be used for dynamic assignment.
One day we might use it to parse \verb+\let+ as well.
<<*>>=
procedure let(lhs, rhs)
  cstab[lhs] := cstab[rhs]
  csclosure[lhs] := csclosure[rhs]
end

procedure let_closure(lhs, cl[])
  csclosure[lhs] := if *cl = 1 then cl[1] else cl
end

procedure letenv(lhs, rhs)
  begintab[lhs] := begintab[rhs]
  endtab[lhs] := endtab[rhs]
  begincl[lhs] := begincl[rhs]
  endcl[lhs] := endcl[rhs]
end
@
\section{HTML formatting}
\label{html-format}

First, generic procedures used to create beginning and ending tags.
<<*>>=
procedure tag(html)
   return "<" || html || ">"
end

procedure endtag(html)
  return "</" || html || ">"
end
@
Next, a gazillion formatting procedures.
<<*>>=
procedure Ccomment(S)
  if *S.comment > 0 then {
    S.text(S, "<!--")
    S.comment ? {
      while S.text(S, tab(find("--"))) do {
        move(2)
        S.text(S, "- - ")
      }
      S.text(S, tab(0))
    }
    S.text(S, "-->")
  }
  S.comment := ""
  return
end
<<*>>=
procedure Cparagraph(S)
  S.text(S, "<p>")
end
<<*>>=
procedure Cmath(S)
  <<take open-group actions>>
  S.text(S, "<i>")
end

procedure Cmath_end(S)
  S.text(S, "</i>")
  <<take close-group actions>>
end
<<*>>=
procedure Cdisplaymath(S)
  <<take open-group actions>>
  S.text(S, "<blockquote><i>")
end

procedure Cdisplaymath_end(S)
  S.text(S, "</i></blockquote>")
  <<take close-group actions>>
end
<<*>>=
procedure Cmakeatletter(S)
  S.csletters ++:= '@'
end

procedure Cmakeatother(S)
  S.csletters --:= '@'
end
@
Approximate \verb+\kill+ by eliminating text.
<<*>>=
procedure Ckill(S, cs, cl)
  S.the_text := ""
end
@ 
\section{Support for adding control sequences dynamically}

The idea is to use formal comments of the form:
\begin{quote}
\verb+% l2h function arg arg ...+
\end{quote}
These comments have the same effect as the procedure calls in
the chunk [[<<control-sequence assignments>>]].
@
Our first step is to create a table with the names of the functions we
recognize.
Ordinarly this table would be distributed, but I created it after the
fact with a little quick Unix pipeline.
<<*>>=
global csfunctions
<<initialization>>=
csfunctions := table()
<<assign to dynamic-add table>>=
csfunctions["argblock"] := argblock
csfunctions["argblockv"] := argblockv
csfunctions["envblock"] := envblock
csfunctions["fontchange"] := fontchange
csfunctions["ignore"] := ignore
csfunctions["ignoreenv"] := ignoreenv
csfunctions["let"] := let
csfunctions["letenv"] := letenv
csfunctions["listenv"] := listenv
csfunctions["substitution"] := substitution
csfunctions["activesubst"] := activesubst
csfunctions["closure"] := let_closure
csfunctions["let_closure"] := let_closure
csfunctions["newcommand"] := l2h_macro
csfunctions["macro"] := l2h_macro
csfunctions["environment"] := l2h_environment
csfunctions["tabular"] := tabular
@
Now, the tough issue is how to parse arguments.  I'm going to try the
following initial strategy:  arguments are separated by spaces.
To put a space within an argument, use \verb+#+.  There is no way to
put a \verb+#+ within an argument.
<<*>>=
global dynamic_add_hack
procedure parse_dynamic_add(S)
   if (optwhite(), =("l2h"|"sl2h"), skipwhite(), 
       p := tab(upto(' \t')), <<make [[p]] a good function or warn and [[fail]]>>, 
       skipwhite(), any(~'\n')) then {
     a := []
     while (any(~'\n'), l := tab(upto(' \t\n') | 0)) do {
       put(a, if p === (l2h_macro|l2h_environment) then l else map(l, "#", " "))
       skipwhite()
     }
     dynamic_add_hack := S
     p!a
     dynamic_add_hack := &null
     return
   }
end
<<make [[p]] a good function or warn and [[fail]]>>=
((p := \csfunctions[p]) | 
{ dynamic_warn(p); fail })
<<*>>=
procedure dynamic_warn(p)
  static badprocs
  initial badprocs := set()
  if not member(badprocs, p) then {
    write(&errout, "Warning: % l2h ", p, " not recognized -- ignored")
    insert(badprocs, p)
  }
end
@     
\section{Miscellanous utilities}
[[optwhite]] skips and returns optional white space.
<<*>>=
procedure optwhite()
  suspend tab(many(' \t')) | ""
end
@ [[skipwhite]] insists that there must be some white space.
<<*>>=
procedure skipwhite()
  suspend tab(many(' \t'))
end
@
\section{Main program for a noweb filter}
First, this is how we use the converter as a noweb filter.
<<l2h.icn>>=
<<*>>
procedure main(args)
  local line
  errstatus := 0
  every arg := !args do
    case arg of {
      "-show-unknowns" : show_unknowns := 1
      "-html-quotes"   : html_quotes := 1
      default : fatal("unknown arg ", image(arg))
    }
  while line := read() do
    apply(filter, line)
  warn_unknown(\unknown_set, "control sequences", "\\")
  warn_unknown(\unknown_envs, "environments", "{", "}")
  if errstatus > 0 then
    write("@fatal l2h Error occurred in l2h conversion")
  exit(errstatus)
end

procedure apply(pass, line)
    line ? (="@" & pass(tab(upto(' ')|0),  if =" " then tab(0) else &null))
end
@
This is noweb filter machinery.  I really ought to coordinate quoted text 
with the converter (so it always shows up in the right place), 
but so far I'm too lazy.
<<l2h.icn>>=
global curfile, curline

procedure filter(name, arg) 
  static S, code
  initial S := converter("V")
###  write("               mode ", S.mode)
  case name of {
    "begin"    : {<<out>>; if match("code ", arg) then code := 1}
    "end"      : {if match("docs ", arg) then <<possible paragraph>>
                  <<out>>; code := &null; S.mode := "V"}
    "quote"    : { outtext("\0" ? convert(S)) }
    "endquote" : { outtext("\1" ? convert(S)) }
    "file"     : {<<out>>; curfile := arg; curline := 1}
    "line"     : {<<out>>; curline := integer(arg)}
    "defn"     : { write("@", name, " ", convert_use_or_def(arg)) }
    "use"      : { write("@", name, " ", convert_use_or_def(arg)) }
    "text"     : {if \code then <<out>> else outtext(arg ? convert(S)) }
    "nl"       : {if \code then <<out>> else outtext("\n" ? convert(S)); curline +:= 1}
    "fatal"    : {<<out>>; exit(1)}
    default    : {<<out>>}
  }
  return
end
<<possible paragraph>>=
if S.mode ~== "V" then write("@text <p>")
@  A special function is needed to implement {\tt noweb}'s quoting 
convention within chunk names.
<<l2h.icn>>=
procedure convert_use_or_def(s)
  r := ""
  s ? {
    while r ||:= quickconv(tab(find("[["))) do {
      (r ||:= ="[[") | fatal("impossible missing [[")
      (r ||:= tab(find("]]")) || tab(many(']'))) |
                fatal("impossible missing ]] in ", image(s))
    }
    return r || quickconv(tab(0))
  }
end

procedure quickconv(s)
  static C
  initial C := converter("H")
  return 1(("{" || s || "}" ? convert(C)), reset(C))
end
<<out>>=
write("@", name, (" " || \arg) | "")
<<l2h.icn>>=
procedure outtext(s)
  s ? 
    while not pos(0) do
      if ="\n" then write("@nl")
      else if ="\0" then write("@quote")
      else if ="\1" then write("@endquote")
      else write("@text ", tab(upto('\n\0\1') | 0))
  return
end
<<*>>=
global errstatus
procedure error(args[])
  errstatus := 1
  return write!([&errout, (\curfile || ":") | "line ", curline, ": "] ||| args)
end
@
\section{Main program for a simple converter}
<<sl2h.icn>>=
<<*>>
global curfile, curline

procedure convert_file(f)
  static S
  initial S := converter("V")
  curline := 0
  while line := read(f) do {
    curline +:= 1
    writes(convert(S, line || "\n"))
  }
  return
end

procedure main(args)
  local warn
  warn := 1
  errstatus := 0
  every arg := !args do
    if arg[1] == "-" then
      case arg of {
        "-show-unknowns" : show_unknowns := 1
        "-nowarn" : warn := &null
        "-html-quotes"   : html_quotes := 1
        "-" : { curfile := arg; convert_file(&input) }
        default : write(&errout, "Warning: unrecognized option ", arg)
      }
    else if f := open(curfile <- arg) then
      convert_file(f)
    else
      write(&errout, "Error: Can't open file ", arg)
  if /curfile then
    convert_file(&input)
  if \warn then {
    warn_unknown(\unknown_set, "control sequences", "\\")
    warn_unknown(\unknown_envs, "environments", "{", "}")
  }
  exit(errstatus)
end
@ 
<<*>>=
procedure fatal(L[])
  write!(["@fatal l2h "] ||| L)
  write!([&errout, "noweb error in l2h: "] ||| L)
  exit(1)
end
@
<<*>>=
procedure rcsinfo () 
  return "$Id: l2h.nw,v 1.24 2008/10/06 01:03:05 nr Exp nr $" ||
         "$Name: v2_12 $"
end
@
\section{Chunks}
\nowebchunks

\begin{multicols}{2}[\section{Index}]
\nowebindex
\end{multicols}
@
\end{document}
