## File: manual.doc

package info (click to toggle)
swi-prolog 3.1.0-2
• area: main
• size: 8,772 kB
• ctags: 12,869
• sloc: ansic: 43,657; perl: 12,577; lisp: 4,359; sh: 1,534; makefile: 798; awk: 14
 file content (787 lines) | stat: -rw-r--r-- 31,963 bytes parent folder | download | duplicates (6)
 123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361362363364365366367368369370371372373374375376377378379380381382383384385386387388389390391392393394395396397398399400401402403404405406407408409410411412413414415416417418419420421422423424425426427428429430431432433434435436437438439440441442443444445446447448449450451452453454455456457458459460461462463464465466467468469470471472473474475476477478479480481482483484485486487488489490491492493494495496497498499500501502503504505506507508509510511512513514515516517518519520521522523524525526527528529530531532533534535536537538539540541542543544545546547548549550551552553554555556557558559560561562563564565566567568569570571572573574575576577578579580581582583584585586587588589590591592593594595596597598599600601602603604605606607608609610611612613614615616617618619620621622623624625626627628629630631632633634635636637638639640641642643644645646647648649650651652653654655656657658659660661662663664665666667668669670671672673674675676677678679680681682683684685686687688689690691692693694695696697698699700701702703704705706707708709710711712713714715716717718719720721722723724725726727728729730731732733734735736737738739740741742743744745746747748749750751752753754755756757758759760761762763764765766767768769770771772773774775776777778779780781782783784785786787 \documentclass[11pt]{article} \newcommand{\runningtitle}{SWI-Prolog's latex2html} \usepackage{pl} \usepackage{html} \makeindex \title{Converting LaTeX into HTML} \author{Jan Wielemaker\\ SWI, University of Amsterdam\\ Roetersstraat 15\\ 1018 WB~~Amsterdam\\ E-mail: \email{jan@swi.psy.uva.nl}} \begin{document} \maketitle \begin{abstract} This document describes a Prolog package for translating LaTeX into HTML documents. It is not a reimplementation of \program{latex2html} in Prolog. Instead of aiming at the production of a HTML document that looks as closely as possible to the original printed version with as little hassle as possible, it aims the simultaneous maintenance of a paper and WEB version of a document. The main virtue of this package is a simple, yet powerful, interface for extending the translator. \end{abstract} \tableofcontents \section{Introduction} Paper and a hypertext browser are different media. For various documents, it is desirable to have both a paper version and a version that can be consulted through the WEB as a hypertext document. For the latter, the document should be represented using HTML. HTML however is not the ideal language for maintaining a document: \begin{itemlist} \item [Not extendable] It is not possible to define macros in HTML, which makes the maintenance of documents in HTML itself difficult. Highly structured documents, such as manuals and reports benefit from a description in the terminology of the domain, which are later translated into domain-independent formatting commands. For example, when writing a Prolog manual, it is better to start the description of a predicate using a formatting command \const{predicate}, rather then directly using textual layout primitives such as list, item, font, etc. \item [Difficult-to-read syntax] This can always be debated, but lets say I don't like it. \item [Not sufficiently rich to specify a quality paper document] Notably spacing, alignment, mathematics and tables are less powerful than one would wish for generating a quality paper document. \end{itemlist} \section{Maintaining a structured document} This toolkit aims first of all at structured documents: manuals, technical report are examples. Such documents tend to describe many instances of domain-specific data. This toolkit assumes the author defines a set of LaTeX macros to map the domain-specific frames into the general text terminology LaTeX uses. In parallel, the user defines translation of these frames into HTML commands. This translation is not necessarily the same. For example, when defining a syntax in BNF, it may be desirable to make links from the usage of BNF terms to their definition. For the paper version, an index of the terms defined is probably the desired cross-referencing aid. \section{Overview} \label{sec:overview} The translator consists of two parts. The first part is a C-program that translates a LaTeX file or string into a Prolog list of TeX tokens. This package also contains the larger part of a pretty-printer for HTML. In between is a Prolog program that translates the LaTeX token list into an HTML token list. For this process, Prolog's unification and non-determinism allow for easy definition of the translator. The translator itself is separated into a number of components, some of which may be extended by the user. \begin{description} \item[Toplevel driver] This component maintains files, options, etc. It is responsible for initialising and controlling the overall process. see latex2html/1. \item[Command and environment translator] Maps individual commands and environments into either plain HTML tokens or HTML macros (see below). This level is represented by the predicates cmd/[2-4] and env/2, which may be extended or redefined by the user. \item[HTML macro expander] Generating plain HTML in one step is cumbersome. The macro expander allows for parameterised expansion of terms into sequences of HTML commands. Of course, macros may be expressed in macros. The set of macros is represented by the \predref{#}{2} predicate. Macros are called using \functor{#}{1} terms. \item[Reference resolver] References to local (i.e.\ inside the document) labels are translated into the appropriate HTML commands. Warnings are printed for undefined references. \item[Pretty printer] The pretty-printer provides the final output. It deletes, maps and translates blank space in the output to arrive at a reasonable looking HTML document. \end{description} \section{Installing the translator} To install the translator, edit first install \url[SWI-Prolog]{http://www.swi.psy.uva.nl/usr/jan/SWI-Prolog.home}, version 2.7.18 or later. Next edit the \file{Makefile} and finally run \program{make} to install the system. Without modifications, the Makefile should work on any system on which SWI-Prolog supports an interface to shared objects and \program{gcc} supports the \cmdlineoption{-shared} option. After successful execution, the program may be run as: \begin{verbatim} % latex2html file \end{verbatim} \section{Running the translator} \subsection{Running LaTeX} If the documents contains \program{BibTeX} references, it should first be processed by \program{LaTeX} and \program{BibTeX} to create the \fileext{bbl} file holding the references. Section numbers, footnotes, cross-references, etc.\ are generated by the translator. Running \program{LaTeX} before using the translator is also useful for finding and fixing \program{LaTeX} syntax errors. The translator checks the syntax, but gives other difficult to understand error messages as \program{LaTeX}. \subsection{Translating to HTML} Normally, the command \begin{verbatim} % latex2html file \end{verbatim} should translate \file{file.tex} into \file{file/file.html}. Separate \fileext{html} files are generated for each section, the table of contents, all (foot)notes and the index, unless the command \texcmd{onefile} appears in the preamble of the document, in which case the entire document is created in \file{file/file.html}. The translator handles \texcmd{include} and \texcmd{input} commands to process LaTeX included files. If a \texcmd{usepackage} command is encountered, the system will look for a corresponding Prolog file to define additional translation rules. The content of packages or \fileext{sty} files in not examined. See \secref{extending}. \subsection{Running the translator from the Prolog toplevel} Notably when testing and extending the translator, it may be wise to run the translator from the Prolog toplevel. The easiest way is to use: \begin{verbatim} % latex2html -pl \end{verbatim} which will start Prolog, set the appropriate library directory, load \pllib{latex2html} and finally enters the Prolog toplevel. After this, it is possible to load additional packages and/or initialise the debugger for debugging the translator. To run the translator, use latex2html/1: \begin{description} \predicate{latex2html}{1}{+InputFile} \arg{InputFile} is the name of the toplevel LaTeX file, either with or without the \fileext{tex} extension. The translator will create a directory using the basename of the \arg{InputFile} for the output. The toplevel HTML output file is constructed from the same basename with the extension \fileext{html}. For example. Suppose your toplevel document is called \file{gnat.tex}. This is translated into \file{gnat/gnat.html} using the following commands: \begin{verbatim} % latex gnat % bibtex gnat % latex2html -pl Welcome to LaTeX2HTML version 0.5 1 ?- latex2thml(gnat). 2 ?- halt. \end{verbatim} \end{description} \subsection{Warnings from the translator} Warnings from the translator come in three flavours. First of all, there are warnings from the tokeniser, either because it does not know about the argument syntax for a command or environment, or because it detects an error in the LaTeX document. For any command or environment it does not know, it assumes the command or environment has no arguments, and prints a warning: \begin{code} [WARNING: Unknown command: \gnat] [WARNING: undefined environment: gnu] \end{code} See \secref{extending} for defining these commands. Next, there are warnings issued by the translator. If a command could nor be translated, it will print a message of the form: \begin{code} Failed to translate \gnat in mode "document" Term: "gnat" \end{code} If this happens, the definition of cmd/[2-4] should be debugged, or extended to deal with the command. The command will be ignored. If an environment could not be processed the env/2 command should be debugged or extended. The warning is: \begin{code} translate_2(env(gnu, [], [\par]), document, ...) failed \end{code} If an HTML macro could not be expanded, the definition of \predref{#}{2} should be examined. The system will warn: \begin{code} Post-processing macro #gnus/1 could not be expanded. \end{code} Finally, if local labels could not be resolved, messages of the format below will be printed: \begin{code} No label for reference "sec:summary" \end{code} \section{Extending the translator} \label{sec:extending} This section defines how the translator may be programmed. It defines the hook predicates available to an extension module, as well as the generic translation predicates that may be called from user-defined hooks. First, we explain how an extension is declared. Normally, a document requiring additional structuring LaTeX macros will start like this: \begin{verbatim} \documentclass[11pt]{article} \usepackage{mymacros} \begin{document} \end{document} \end{verbatim} The file \file{mymacros.sty} will include additional packages required, dedicated style settings, structuring macros, etc. The latex2thml translator will not examine the contents of this file. Instead, it will search for \file{mymacros.pl} to find a Prolog module defining the additional translation rules. It will first use the \const{tex} path alias, and then try the \const{library} path alias. If successful, this file will be loaded into the \const{user} module using the Prolog predicate ensure_loaded/1. If the file cannot be located, it is silently ignored. The typical structure of the extension file is: \begin{verbatim} :- module(, []). :- use_module(library(latex2html)). :- latex2html_module. :- tex_load_commands(pl). \end{verbatim} The directive latex2html_module/0 registers the module as a module containing additional rules for latex2html. These rules will be tried {\em before} any other rules. Alternatives need not be cut on any of the hook predicates, as this is done immediately by the translators main control loop. If you want to redefine a rule only under specific circumstances, simply make sure the clause only succeeds in those cases that redefinition is desired. It is generally not (yet) possible to wrap' the existing translation rule. It is not required to define clauses for all extension hooks. \subsection{Specifying the LaTeX syntax for the tokeniser} \label{sec:cmdspec} The C-defined LaTeX tokeniser needs to know about the argument syntax for each of the LaTeX commands used in the document. The syntax of commands is defined in \fileext{cmd} files. The initial definition is in the file \file{latex.cmd}. Blank space is ignored, and the \% sign starts a comment field that lasts till the end of the current line, just as with LaTeX itself. A command declared using a line of the form: \begin{tabular}{lrll} \isa \const{\} { } [\const{=}] & \\ \isa \verb${$ \verb$}$ & \\ \ora \const{[} \const{]} & \\ \isa \const{-} & Do not tokenise \\ \ora \const{+} & Tokenise argument \\ \ora \const{d} & Argument is a dimension \\ \isa \const{verb} & Act as \texcmd{verb} \\ \ora \const{begin} & Act as \texcmd{begin} \\ \ora \const{end} & Act as \texcmd{end} \\ \ora \const{item} & Separate items in a list \\ \ora \const{prolog} & Call prolog_function/1 immediately \\ \end{tabular} An environment declaration is of the form: \begin{tabular}{lrll} \isa \verb${$ \verb$}$ [\const{=}] & \\ \isa \const{verbatim} & Act as a verbatim environment \\ \ora \const{list} & My body consists of items \\ \ora \const{float} & I am a floating environment \end{tabular} Command specification files are normally loaded from the Prolog extension files using the predicate tex_load_commands/1. \subsection{The HTML token list} \label{sec:htmltokens} The output of the translator is a list of HTML tokens. This section describes the tokens that are recognised by the pretty printer. \begin{description} \termitem{html}{Command} Literally outputs the given command. No spaces are inserted in the output, neither before nor after the command. \termitem{ref}{Label} Expands to the number associated with \arg{Label}. Thus, if \arg{Label} appeared in a section, this is the section number. If \arg{Label} appeared in a figure or table, this is the number of the figure or table. \termitem{label}{Label, Text, Ref} Outputs \exam{\arg{Text}}. \termitem{lref}{Label, Text} Outputs \exam{\arg{Text}}. is the file to which the section containing \arg{Label} has been (or will be) written. See label/3. \termitem{lref}{fileof(Label), Text} Outputs \exam{\arg{Text}}. is the file to which the section containing \arg{Label} has been (or will be) written. See label/3. \termitem{iflref}{Arg} As \term{lref}{Arg}, but emits nothing if the label is not defined. For example, the page-header uses this construct to refer to to table of contents, the summary and the index. If one of these does not exist, the corresponding link is not created. \termitem{lforw}{Label, Text} Creates an anchor, just like \functor{lref}{2}, but gives the anchor the attribute \exam{NAME="back-to-\arg{Label}"}. Together with \functor{lback}{2}, this forms a \idx{bi-directional link} between two anchors. \termitem{lback}{Label, Text} The other end of the \functor{lforw}{2} link. It is used for handling footnotes. \termitem{cite}{Key} Translated from the LaTeX \texcmd{cite} command. It will lookup \arg{Key} in the cite/2 predicate, and emit the label for the key, rather then the key itself. The output format depends on the BibTeX style used. \termitem{yearcite}{Key} As \term{cite}{Key}, but only emits the year of the label. \termitem{tableofcontents}{document} Emits the entire table of contents of the document in this place. \termitem{tableofcontents}{section(\arg{Tag})} Emits the table of contents of all subsections of the indicated section. Normally used to create the footer for sections that have subsections. \termitem{tell}{FileBaseName} Divert further output to the named file. \arg{FileBaseName} is only the basename of the output file, i.e. without trailing \fileext{html} or leading directory. This is the only way to switch output files. The output is scanned for functor{tell}{1} terms and \functor{label}{3} terms for building the label/3 predicate, which in turn is used for outputting the proper reference names for labels. \termitem{verb}{Text} Output \arg{Text} without any interpretation of spaces and newlines. The HTML special characters (\verb$<>&$) are automatically mapped to the required escape sequences. \termitem{verbatim}{Text} Same as \functor{verb}{1}. \termitem{nospace}{Atom} Output atom, translating the HTML special characters. Do not insert spaces before or after the word. \termitem{}{} Atoms or SWI-Prolog strings are treated as a {\em word}. HTML special characters are translated. If two words are emitted adjecently, a space or newline (for line-wrap) is inserted between them. No spaces are inserted between any of the other forms and a word. \end{description} \subsection{The macro expander} \label{sec:htmlmacros} The macro expander is implemented by macro_expand/2 and is called by the toplevel driver after any successfully translated command or environment. \begin{description} \predicate{macro_expand}{2}{+In, -Out} The input is a (nested) list or a single HTML token or a macro reference (terms of \functor{#}{1}, \functor{+}{1} or \functor{+}{2}). The \arg{Out} is a (nested) list of HTML tokens as described in \secref{htmltokens}. \end{description} The translator translates terms using the following syntax: \begin{description} \termitem{+}{Tokens} \arg{Tokens} is a list of raw LaTeX tokens, and the translator is called recursively as \exam{translate(\arg{Tokens}, normal, \arg{Out})}. \termitem{+}{Mode, Tokens} As \functor{+}{1}, translating in mode \arg{Mode} rather then \const{normal}. \termitem{#}{MacroCall} Calls \predref{#}{2} to expand the macro. \end{description} The following macros have been predefined: \begin{description} \termitem{tell}{File} If \texcmd{onefile} is specified in the header, do nothing, else emit \term{tell}{File} to divert subsequent output to the named file. \termitem{thetitle}{} Contains the document title defined by the LaTeX \texcmd{title} command. \termitem{theauthor}{} Contains the document author defined by the LaTeX \texcmd{author} command. \termitem{title}{Title} Defines the HTML document title using the \HTML{TITLE} tag. \termitem{defitem}{Label} Definition-list item. Translates to \exam{

\arg{Label}
}. \termitem{var}{Var} Indicates a variable. Translates to \exam{\arg{Var}}. \termitem{code}{Text} Indicates code in running text. Translates to \exam{\arg{Text}}. \termitem{pre}{Text} Preformatted multiline text. Translates to \exam{\arg{Text}}. \termitem{xmp}{Text} Preformatted multiline example. Translates to \exam{\arg{Text}}. \termitem{strong}{Text} Emit \arg{Text} as extra emphasized text (normally printed {\bf bold}). Translates to \exam{\arg{Text}}. \termitem{em}{Text} Emit \arg{Text} as emphasized text (normally printed {\em italic}). Translates to \exam{\arg{Text}}. \termitem{b}{Text} Emit \arg{Text} as bold text. Translates to \exam{\arg{Text}}. \termitem{i}{Text} Emit \arg{Text} as italic text. Translates to \exam{\arg{Text}}. \termitem{center}{Text} Emit \arg{Text} centered. Translates to \exam{
\arg{Text}
}. \termitem{quote}{Text} Emit \arg{Text} as a quote. Translates to \exam{
\arg{Text}
}. \termitem{embrace}{Text} Emit \arg{Text} between "()" braces. Translates to \exam{(\arg{Text})}. \termitem{embrace}{"AZ", Text} Emit \arg{Text} between "AZ" braces. Translates to \exam{A\arg{Text}Z}. \termitem{h}{Level, Text} Emit a header. Translates to \exam{\arg{Text}}, where \arg{N} is \arg{Level}. \termitem{row}{Columns} Emits a row of a table. Translates to \exam{
...
\arg{C1}}. \arg{Columns} is a list containing the HTML code for each column in the row. \termitem{label}{Label, Text, Tag} Emits \term{label}{Label, Text, Tag}, but canonises the \arg{Label} and \arg{Text} fields first. \arg{Tag} is the tag of the current section or float. \termitem{label}{Label, Text} As \term{label}{Label, Text, Tag}, but emits a label not related to a section or float. \termitem{lref}{Label, Text} Emits \term{lref}{Label, Text}, but canonises the \arg{Label} and \arg{Text} fields first. \termitem{iflref}{Label, Text} Emits \term{iflref}{Label, Text}, but canonises the \arg{Label} and \arg{Text} fields first. \termitem{lback}{Label, Text} Emits \term{lback}{Label, Text}, but canonises the \arg{Label} and \arg{Text} fields first. \termitem{lforw}{Label, Text} Emits \term{lforw}{Label, Text}, but canonises the \arg{Label} and \arg{Text} fields first. \termitem{url}{URL, Text} Emits an external URL: \exam{\arg{Text}}. \termitem{cite}{Keys} Handle a \texcmd{cite} command. \arg{Keys} is translated into a sequence \mbox{\term{cite}{Key1}, ',', ' ', \ldots} and the whole is enclosed in \exam{ \ldots }. \termitem{opencite}{Keys} Currently as \term{cite}{Keys} \termitem{yearcite}{Keys} As \term{cite}{Keys}, but emits \term{yearcite}{Key}. \termitem{header}{Tag} Produce a header for the file containing section \arg{Tag}. This macro may be redefined to modify the section header. \termitem{header} Produce a header for a file not defining a section. \termitem{footer}{Arg} Produce a footer for the file containing section \arg{Tag}. This macro may be redefined to modify the section header. Normally, this macro creates a local' table of contents for all subsections of this section (or nothing if there are no subsections). \end{description} \subsection{User extension hook predicates} \label{sec:extpreds} As discussed in \secref{overview}, the translator may be extended at various levels. Normally, is should suffice to extend the definitions of cmd/[2-4], env/2, list_command/4 and \predref{#}{2}. They are defines below. \begin{description} \predicate{cmd}{4}{+Command, +ModeIn, -ModeOut, -HTML} Translate the given \arg{Command}. A command is represented by a term of the format \term{}{, \ldots}. Each is a term of the form \exam{\{\}} if it is an obligatory argument. If it is an option argument and not specified, is the empty list (\const{[]}). Otherwise it is a list holding a single element representing the argument. If the command defines an optional modifier (as the \texcmd{section} command to suppress the section number), this is translated into the first argument to the \arg{Command}, which is either bound to the atom \const{*} if the modifier was specified, or \const{-} of not. If the command argument is specified as \const{-} or \const{d} (see \secref{cmdspec}), the tokeniser returns the verbatim text of the argument as a SWI-Prolog string. Otherwise, if the specifier is \const{+}, the argument is a list of LaTeX tokens. For example, the \texcmd{url} command is defined as \begin{code} \url[+]{-} \end{code} and the command \verb$\url[SWI-Prolog]{ftp://swi.psy.uva.nl/pub/SWI-Prolog}$ will be handed to cmd/4 as: \begin{code} url([[SWI-Prolog]], {'ftp://swi.psy.uva.nl/pub/SWI-Prolog'}) \end{code} \arg{ModeIn} specifies the mode of the translator. Only a few values are defined and have defined behaviour: \begin{description} \termitem{math}{} We are processing a LaTeX math environment. \termitem{group}{Font} Used to translate \exam{\{\ldots\}}, possibly holding font switches, as well as other grouped environments, such as \texcmd{mbox} and the cells of a table (\texenv{tabular}). \termitem{\arg{ListName}}{} When processing a list (see list_command/4), the mode is the name of the list environment. This allows for the item commands to consider the list environment in which they are active. \end{description} \arg{ModeOut} defines the mode for further processing. Currently, cmd/4 only implements the font-switches to manipulate the argument of the \functor{group}{1} mode term. \predicate{cmd}{3}{+Command, +Mode, -HTML} Version of cmd/4 that does not need to change modes, but realises mode dependent commands. Example are the \texmode{math} commands. This translator will only be called {\bf after} cmd/4 fails. \predicate{cmd}{2}{+Command, -HTML} Version of cmd/4 that does not change, nor verify the current mode. This translator will only be called {\bf after} cmd/3 fails. \predicate{env}{2}{+Environment, -HTML} Expand an entire environment, i.e.\ from \texcmd{begin} upto and including the matching \texcmd{end} command. \arg{Environment} is a term of the form \term{}{[, \ldots], }. describes the environment arguments (as the column specifier for a \texenv{tabular} environment), while is a list of LaTeX tokens, describing the contents of the environment. Note that \texenv{document} is an environment as well, containing the entire document. Redefining the document environment provides the opportunity for pre- and post-processing of the entire document. Environments that are flagged with the \const{list} type (see \secref{cmdspec}) are handled by a default translator. See list_command/4. \predicate{list_command}{4}{+ListName, +Mode, -OpenHTML, -CloseHTML} If env/2 traps an environment marked as \const{list}, it will break the environment into items by scanning for commands flagged as \const{item}, output the \arg{OpenHTML} code, process the items and add the \arg{CloseHTML} code. Below is the default definition of this predicate. Note that, as always, the HTML output is either a simple HTML token, an HTML macro, or a (nested) list of these. \begin{code} list_command(description, _, html('
'), html('
')). list_command(itemize, _, html('
'), html('
')). list_command(enumerate, _, html('
'), html('
')). list_command(thebibliography, _, html('
'), html('
')). \end{code} \predicate{#}{2}{+Macro, -Expansion} This predicate defines the macro-expander as invoked through the macro_expand/2 command. \arg{Macro} is an arbitrary Prolog term, possibly containing variables to act as macro arguments, \arg{Expansion} is the expansion. The expansion is an arbitrary HTML token list, possibly containing references to other macros. Recursive processing of the same macro is possible, but there is no guarding against infinite loops. See \secref{htmlmacros} for the default macro-definitions available. The usage of these macros is highly encouraged, both to keep the translator simple and to provide sharing of definitions. \end{description} \subsection{Translation support predicates} This section describes the public predicates of \pllib{latex2html}. These predicates are available to the extension hooks to realise the desired translation. \begin{description} \predicate{welcome}{0}{} Simply prints the package banner message. \predicate{translate}{4}{+In, +ModeIn, -ModeOut, -Out} Call the general translator for a list of LaTeX tokens. \arg{ModeIn} is the starting mode, \arg{ModeOut} is the exit mode. \arg{Out} is unified with a (nested) list of HTML tokens. Note that the hook predicates can return \term{+}{TeXTokens}. If this construct is detected in the output of cmd/[2-4] or env/2, the translator is called automatically. \predicate{translate}{3}{+In, +ModeIn, -Out} As translate/4, but does not return the final mode. \predicate{latex2html_module}{0}{} Register the calling module as an extension module module for the translator. All hooks will be called in the reverse order of these registrations, ending with the built-in translation rules. \predicate{tex_input_directory}{1}{+Dir} Register \arg{Dir} as a directory for finding LaTeX files. The initial directory is \file{.}. If the variable \env{TEXINPUTS} is defined, the initial directory list is read from this variable. The definition of the input files is maintained using in the user:file_search_path/2 alias \const{tex}. Files are located using absolute_file_name/3. \predicate{step_counter}{2}{+Name, -Value} Step the indicated counter. Available counters are \const{figure} and \const{table}. The returned value is the new value of the counter. The first call returns 1. \predicate{ps2gif}{3}{+In, +Out, +Options} Translate a \idx{PostScript} figure into a \idx{GIF} figure. Incomplete. Please see the source for the current definition. \predicate{translate_command}{4}{+In, +ModeIn, -ModeOut, -HTML} Translate an individual command in the form as passed to cmd/[2-4]. May be used to express the translation of a command in terms of the translation of another. \predicate{translate_environment}{4}{+In, +ModeIn, -ModeOut, -HTML} As translate_command/4, but for the translation of environments. \predicate{translate_reference}{4}{+TextLabel, +RefPrefix, +Label, -HTML} Used for the translation of \texcmd{secref}, etc. The output will be \arg{TextLabel}~\arg{Tag}, where \arg{Tag} is the tag-number of the section or float of the target label. The label searched for is \exam{\arg{RefPrefix}:\arg{Label}}. \predicate{translate_footnote}{2}{+Text, -HTML} Create a footnote. It will output a reference to the node and remember the \arg{Text} to emit the final footnote. \predicate{current_setting}{1}{+Name(-Value, \ldots)} Request a setting for the translator. Currently defined: \begin{description} \termitem{keep_figures}{} For figure translation. If this test succeeds, the old translation should be kept. \termitem{html_output_dir}{Dir} Unifies \arg{Dir} with the directory to which the output files are written. \end{description} \predicate{do_float}{2}{+FloatType(+Number), +Goal} Run \arg{Goal}, such that labels will refer to the number of the float environment (figure, table). So, when processing the contents of a figure environment, step the figure counter, and process the body: \begin{verbatim} ..., step_counter(figure, Fig), do_float(figure(Fig), ( translate(...), ... )), ... \end{verbatim} \predicate{tex_load_commands}{1}{CmdBaseName} Load a file holding LaTeX command declarations for the tokeniser. See \secref{cmdspec}. The file normally has extension \fileext{cmd} and is searched for in the same directories as extension Prolog files (\const{tex} and \const{library}). \predicate{add_to_index}{2}{+Index, +Label} Add \arg{Index} to the index. \arg{Label} is the place from which the item is referenced. If \arg{Label} is a term \term{+}{Label}, it is considered the {\em principal} reference, and the word in the index itself will be rendered as a hyper-link to the principal location. \predicate{clean_tt}{2}{+Raw, -CleanAtom} When writing manuals, it is often necessary to use TeX special commands for specifying the TeX special characters. For example, to get a nice, not mathematical tilde, without using \texcmd{verb}, so it can be used as a command argument, one should use \verb${\tt\string~}$. This predicate eliminates all these special constructs to arrive at an atom describing the plain character sequence. \end{description} \subsection{Dynamic predicates for maintaining cross-referencing} The predicates below are dynamic predicates maintained by the translator to deal with cross references. They are currently internal to the translator, but described anyhow as they are referenced in this document. \begin{description} \predicate{label}{3}{Label, File, Tag} Built after the initial translation by scanning the output token list for terms of the form \functor{tell}{1} (for keeping track of the current file), \functor{label}{3} \functor{lback}{2} and \functor{lforw}{2}. Used by the final output stage. \predicate{cite}{2}{Key, Cite} Built from processing \texcmd{bibitem} commands from the \fileext{bbl} file. Used by \texcmd{cite} to insert the proper reference to the bibliography. \end{description} \section{Problems and limitations} The current translator is not very complete. It is likely that HTML version 3 will allow us to complete the translation in many respects, notably handling more then just the very basic math symbols. Sofar the translator has been used to translate the \url[SWI-Prolog manual]{http://www.swi.psy.uva.nl/usr/jan/SWI-Prolog/Manual/Title.html} and the XPCE (GUI package for Prolog) \url[User Guide]{http://www.swi.psy.uva.nl/projects/xpce/UserGuide/Title.html} and the PHD thesis \url[Cognitive Tools]{/staff/jan/anja/main/main.html}. \printindex \end{document}