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%\iffalse This is patch.doc, and it's -*-LaTeX-*- text
%% patch.doc/patch.tex
%% (c) 1994 by David Kastrup (dak@pool.informatik.rwth-aachen.de)
%% Version 0.91
%% Redistribution of patch.doc is allowed, provided it is not modified
%% in any way. The stripped version patch.tex may only be distributed
%% as part of other packages, and only if the unstripped version
%% is distributed on demand.
% Stripping is to be done by removing all lines starting with a single
% percent sign.
% You may extract a driver file for printing the documentation with
% the doc style package by extracting all lines starting with
% %<+driver>, while removing the %<+driver> directive.
%\fi
% \CheckSum{360}
% \title{Using {\tt patch.tex}}
% \author{David Kastrup\\dak@pool.informatik.rwth-aachen.de}
% \date{January 22, 1994}
% \maketitle
% \MakeShortVerb\"
% \begin{abstract}
%   Often one has the need to use a preestablished format, such
%   as~\LaTeX, but with some slight changes to some of the macros.
%   Of~course, it is possible to just copy the offendin maco
%   definitions into your application or style file, and~modify them
%   there. This can lead to parts of your macros being from different
%   versions of \LaTeX{} resp.~\TeX.
%
%   This input file is a tool for replacing just parts of existing macros
%   by user defined parts. If those parts are no longer recognizable,
%   an~error message is produced, calling the user to~attention.
% \end{abstract}
% \tableofcontents
% \section{User Interface}
% The macros defined here will allow ``patching'' up already existing
% macros. A~typical example, included from a~style file used for
% typesetting Greek text (to~appear in "kdgreek") is the following:
%\begin{verbatim}
%\input patch.tex
%\ifx\descriptionlabel\undefined\else
%\gpatch\descriptionlabel#1{{#1}}{%
%    \bf {\grbf}} \fi
%\ifx\@part\undefined\else
%\gpatch\@part[#1]#2{[#1]{#2}}{%
%    \bf\partname~{\grbf\partname\nobreak\ }%
%    \bf {\grbf}} \fi
%...
%\endpatch
%\end{verbatim}
%This shows almost all features that are really there. You start by
%inputting "patch.tex". This, among other things, opens a~local
%group in which all of the definitions of~"patch.tex" are read~in.
%In~order not to use up unnecessary hash~space, almost all local
%commands are in the form~"\^^80" and upwards. For this reason,
%you cannot {\em use\/} any macros of yours with such names
%(Note: they are {\em
%not\/} active characters, but rather regular one-letter control
%sequences), and you should not patch them, but you can patch any
%macros containing them, or patch them into macros.
%
%One macro is {\em very\/} special and must not appear in any macro
%you patch, nor in any arguments to~"\patch": this is~"\@ndp@tch".
%
%\DescribeMacro{\patch}
%\DescribeMacro{\gpatch}
%You follow the "\input" by several "\patch" or "\gpatch"
%commands. These commands
%consist of several parts:
%\begin{itemize}
%\item[Optional "\bslash long"] for definition of macros possibly containing
%  "\par" tokens in their arguments. Note that the prefixes "\global"
%  and~"\outer" are not supported. "\global"ness is achieved by~usage
%  of~"\gpatch" as opposed to~"\patch", and is explained later, and
%  "\outer" macros are detestable.
%\item ["\bslash patch" or "\bslash gpatch"] To be expected.
%\item [\meta{Argument list}] which is the argument list the macro will
%  have in the patched version (usually the same as the original one).
%  It~is terminated by the opening brace of
%\item [\meta{Argument replacement}] which is enclosed in braces. This
%  is fed as an argument list into the old macro, in order to get the
%  replacement text for the new macro. Basically this means that you
%  will have to use, say, "{#1}" for an undelimited parameter~"#1",
%  "#1@" for a delimited parameter "#1@", and "@$#!?!!" for a brace
%  delimited parameter "#1#{" (don't try patching any macros like
%  that. Presume you have never heard of~them).
%\item [\meta{Substitution list}] This contains a~brace enclosed list
%  of~replacements. Each replacement consists of
%  \begin{itemize}
%  \item [\meta{Matching sequence}] which is a sequence of tokens not
%    containing any braces. If really need to match braces, you can
%    match by using implicit braces you get by saying something like
%    "\let\openbrace={". If you think of using the default implicit
%    braces "\bgroup" and~"\egroup", forget~it. They are used in
%    several macros we might want to~patch, and thus are disabled
%    by~default.
%  \item [\meta{Replacement sequence}] which is enclosed in~braces.
%    Again, if you want braces to appear in your replacement, you can
%    make that happen by using implicit braces. Matched braces,
%    however, you may include explicitly.
%  \end{itemize}
%\end{itemize}
%\DescribeMacro{\endpatch}
%Then the patches are followed by~"\endpatch", which closes the group
%opened by~"\input", thus freeing up almost all \TeX{} space
%"patch.tex" took up. Since~mismatched patches can be hard to
%diagnose, "\endpatch" is defined as being~"\outer". As~long as
%the "\outer" nuisance prevails, we~might use it for what it~is
%useful~for.
%
%That's all there is to it! Except for the "\global" issue we promised
%to explain\dots{}
%Usually you will be patching macros of some style, and there will be no
%point in using~"\patch" instead of~"\gpatch". So~mostly "\gpatch" does
%no harm, and will cause a~global definition. "\patch", on the other
%hand, has the problem that its definitions should hold in the group
%ended by~"\endpatch", but not globally. So~"\patch" cannot just make
%the definitions. Instead, it collects the new definitions, and~does
%them all at~"\endpatch".
%
%\DescribeMacro{\globaldefs}
%Here is one friendly feature: If "\globaldefs" is negative,
%"\gpatch"~will invoke "\patch" instead of its own behaviour, so that
%local patches will be performed instead of none at~all (since the then
%non-global definition would disappear at~"\endpatch"). This feature was
%deemed desirable\footnote{Reason:
%I~made an example file showing the effects of several
%"\bslash documentstyle" commands with my Greek macro set. The Greek style
%patched up some \LaTeX{} macros, and this was wanted only
%locally, namely for the length of the demonstration of one particular
%document style.}.
%\subsection{Things to beware of (aka bugs)}
%"patch.doc" is a very simple package (sort~of). It can fail for
%a~number of reasons, and is not applicable in every situation. You
%will have problems if
%\begin{enumerate}
%\item You use implicit tokens which are implicit at the time the
%  patches are applied. "\bgroup" and~"\egroup" are explicitly disabled
%  for this reason. Implicit spaces will be regarded as explicit ones
%  by~"\patch". Implicit macro parameter characters I~am not so sure
%  about. \TeX~behaves pretty wierd with regard to them anyhow. Other
%  implicits should do no~harm. "\patch"~will take the problematic
%  implicit
%  tokens for explicit ones while it is analyzing tokens. It analyzes
%  both matching and replacement tokens, and all tokens in the original
%  macro up to the last replacement performed. This means that, for
%  example, matching implicit braces in locations where you did not
%  intend it can lead to mismatched explicit braces and lots
%  of~confusion.
%\item You use outer tokens in any respect.
%  "\patch" does not care for them.
%\item When "\@ndp@tch" appears anywhere, namely in a~macro to be
%  patched, or in a matching or replacement sequence. It~is used for
%  internal purposes, and you can cause lots of confusion when
%  using~it. This means, for one thing, that you should not try
%  "\patch"ing up any macros of this package with itself.
%\item And this is harsh: if the macro you patch contains "#" marks
%  (which originally were produced by writing "##") these will not be
%  reduplicated, leading to missing parameter number errors (which will
%  do the right thing if you ignore them, but that's ugly), or to
%  recombination with a following number, which is plain wrong. You can
%  work around this ugliness in an~ugly way: specify a~replacement
%  "#{##}" for any such token. I~am pretty much afraid I~know no
%  better way around this one.
%\item Since "\bgroup" and~"\egroup" are disabled, using any macro that
%  in turn uses those will not work while in patch~mode. What
%  I~guarantee to keep working in future versions is "\let" (locally,
%  for making implicit tokens),
%  all expandable constructs (like conditionals) not
%  using any of the macros of this package, and~"\patch"es.
%  Other things are not necessarily supported in patch~mode.
%  Specifically, do not use "\def" or~"\gdef", since manipulation of
%  localness might unnecessarily be thwarted if you~do.
%\item Do not change "\toks@" in any way, or use a~macro changing it.
%  Cannot happen really, if you listen to the last advice.
%\item Do not rely on the patches either taking place or not before the
%  final "\endpatch"! This means, do not use a~patched macro before
%  "\endpatch" in ways which require specifically the patched or
%  the unpatched version. For example, do not patch one and the same macro
%  with two separate "\patch" commands in the same patch session! The
%  reason for this is the collecting behaviour for non-global patches.
%  And you never really know when a~package of yours might come handy
%  non-globally.
%\item For similar reasons,
%  do not use "\input patch.tex" in a local group when you are doing
%  "\gpatch"es (unless you know what you are doing, as in the case of
%  negative~"\globaldefs"). It~might get to~being a~problem sometime.
%\item Never set "\globaldefs" to a~non-zero {\em positive\/} value
%  while working with~"\patch", since it will interfere disastrously with
%  "patch.tex"'s internals, which heavily work with local groups.
%  Anyway, "patch.tex" is by its nature intended for local use only.
%\item Just as a note aside: it is a~very bad idea to set "\globaldefs"
%  to non-zero values longer than strictly necessary. It is especially
%  a~bad idea to set it to a~negative value while {\em typesetting\/}
%  anything,
%  because the output routine (implicitly enclosed in a~group) will
%  never be able to get anything done permanently, and will therefore
%  be repeated over and~over.
%\end{enumerate}
%
%Ok, this should be all there really is to it. If I~look that list over
%again, it seems like groups really occupy my fantasy.
%
%Happy "\patch"ing!
%\StopEventually{\PrintIndex}
%\section{The Implementation}
%We begin by opening our local group and making private control
%sequences accessible:
%    \begin{macrocode}
\begingroup
\catcode`@=11
%    \end{macrocode}
%We then set "\toks@" to the initial set of~actions to~perform at the
%end of the~patches.
%    \begin{macrocode}
\toks@={\endgroup}
%    \end{macrocode}
% \begin{macro}{\endpatch}
%    Rather simple. "\outer"~seems not to do much harm here. It might
%    help better pinpointing severe failures when using~"\patch".
%    \begin{macrocode}
\outer\def\endpatch{\the\toks@}
%    \end{macrocode}
% \end{macro}
% \begin{macro}{\futuredef}
%    This is somewhat similar to "\futurelet", only not at~all. It
%    defines the macro which is its first argument as~code which can
%    by use of~"\aftergroup" reproduce the third argument~token,
%    and after doing that it will call the second argument.
%    All~arguments are removed from the input, unlike "\futurelet"'s
%    behaviour.
%    \begin{macrocode}
\def\futuredef#1#2{\begingroup
%    \end{macrocode}
%    We do this locally, and set up a few things to do after the
%    group. Since a~"\def" is going to finish what we want, we can
%    insert the ``do-after'' token via "\afterassignment".
%    \begin{macrocode}
     \aftergroup\afterassignment \aftergroup#2%
     \aftergroup\def \aftergroup#1%
         \futurelet\next\^^90}
%    \end{macrocode}
% \end{macro}
%    We still have the token in our input stream, but also a copy of
%    its meaning in "\next". We first try out some cases which will
%    not allow us to treat the next token as an undelimited macro
%    parameter. Of course we cannot distinguish explicit from implicit
%    tokens, but we rely on the user to explicitly unimplicate possibly
%    implicit characters. We will do this ourselves with the following
%    two ones:
%    \begin{macrocode}
\let\bgroup\relax   \let\egroup\relax
%    \end{macrocode}
%    Now we start checking all problematic cases.
%    "\^^90" will substitute an appropriate definition given
%    explicitly instead of the following token. If we can, however, we
%    rather use the token we get. If you wonder about this name, here
%    is why: we have to use hosts of macros because of various
%    "\futurelet"-like constructions. Patches occur just in a local group,
%    and should not permanently require resources. If we did not use
%    one-letter control sequences here, the hash table size would be
%    somewhat reduced, permanently, because entries never leave the
%    hash table. One letter control sequences, however, are not
%    hashed, and can disappear without a trace again.
%    \begin{macrocode}
\def\^^90{%
    \ifcat\noexpand\next{%
         \^^91{\aftergroup{\iffalse}\fi}%
    \else\ifcat\noexpand\next}%
         \^^91{\iffalse{\fi\aftergroup}}%
    \else\ifcat\noexpand\next\space
         \^^91{\expandafter\aftergroup\space}%
    \else\ifcat\noexpand\next##
         \^^91{\aftergroup########}%
    \else
         \let\next\^^93%
                 \fi\fi\fi\fi\next}
%    \end{macrocode}
%    "\^^91" is rather simple. We save the definition in
%    "\next@", and we'll call upon this after disposing of the next
%    token.
%    \begin{macrocode}
\def\^^91#1{\def\next@{\endgroup{#1}}%
    \let\next\^^92}
\def\^^92{\afterassignment\next@ \let\next= }
%    \end{macrocode}
%    "\^^93" will actively get the next token, and produce an
%    "\aftergroup" definition from that. It is "\long" in case we are
%    dealing with a "\par" token.
%    \begin{macrocode}
\long\def\^^93#1{\endgroup{\aftergroup#1}}
%    \end{macrocode}
% \begin{macro}{\@ndp@tch}
%    This is supposed to be used as a delimiter. So that we may
%    check for its appearance conveniently, we define it as its own
%    "\futuredef" expansion.
%    \begin{macrocode}
\def\@ndp@tch{\aftergroup\@ndp@tch}
%    \end{macrocode}
% \end{macro}
% \begin{macro}{\gpatch}
%     This is it. If you are in doubt as to what the "\def\next{}" is
%     supposed to~achieve, this is~easy. We want to detect whether you
%     want a~long macro to be~patched. In that case, you say
%     "\long\gpatch"\dots. We can figure this out by comparing
%     "\next" to the non-long~"\empty". Of course, we do not
%     explicitly check for "\outer"ness. You should not even think of
%     wanting to make an "\outer" definition.
%
%    We start by defining~"\gpatch", which will in the case
%    of~disabled "global"ness revert to~"\patch". Both~"\patch"
%    and~"\gpatch" define "\next" as a~macro getting one
%    "\@ndp@tch"-delimited argument:
%    it is all what should appear after a~"\def".
%    "\next"~should make all necessary actions for doing
%    the~definition. After setting~up "\next", "\^^a0"~is called, for
%    which we wrap up the argument list as a~separate argument.
%    \begin{macrocode}
\def\gpatch{\ifnum\globaldefs<\z@
                \expandafter\patch
            \else
                \expandafter\^^98%
            \fi}
\long\def\^^98#1#2#{\def\next{}%
               \long\edef\next##1\@ndp@tch%
                  {\ifx\next\empty\else\long\fi\gdef##1}%
               \^^a0#1{#2}}
%    \end{macrocode}
% \end{macro}
% \begin{macro}{\patch}
%    "\patch"~is a~bit more complicated, because we need to~make
%    additions to the current "\toks@"~list.
%    \begin{macrocode}
\def\patch#1#2#{\def\next{}%
  \long\edef\next##1\@ndp@tch
     {\toks@ \noexpand\expandafter {\noexpand\the \toks@
          \ifx\next\empty\else\long\fi \def##1}}%
  \^^a0#1{#2}}
%    \end{macrocode}
% \end{macro}
%
%    Now the real fun starts. We get the argument replacement list,
%    and the macro body replacement list. We define a~macro~"\^^e0"
%    (the "e" means error) just for knowing the proper macro name for
%    error messages.
%
%    We prepare in a local
%    "\toks@" the definition (because we could not simply
%    "\aftergroup" the argument replacement, which could consist of
%    any number of~tokens). Note that we start yet another group,
%    making the definitions of "\toks@" and "\next" stable.
%
%    \begin{macrocode}
\long\def\^^a0#1#2#3#4{\begingroup
    \def\^^e0{#1}%
    \toks@{\endgroup\next#1#2}%
    \begingroup
    \aftergroup\the\aftergroup\toks@
%    \end{macrocode}
%    We collect the replacement in a continually shrinking token list.
%    Do not get annoyed, but we'll use "\toks@" for that, too.
%    When we are through with replacements, we'll say "\endgroup",
%    after which the definition takes place.
%
%    The replacement needs
%    to be in a token list instead of a macro in order not to break upon
%    encountering hash marks. The use of "\toks@" for this does not
%    conflict with its other uses due to the grouping.
%
%    After that, we are ready to start the fun by expanding our macro,
%    and putting~"\p@check" to~work.
%    \begin{macrocode}
    \toks@{#4}%
    \expandafter\p@check\expandafter{#1#3}\@ndp@tch}
%    \end{macrocode}
% \begin{macro}{\p@match}
% \begin{macro}{\p@replace}
%    These are token lists holding the current string to be matched
%    next, and its replacement string. We
%    use token lists~1 and~2 for that.
%    \begin{macrocode}
\toksdef\p@match=\@ne
\toksdef\p@replace=\tw@
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \begin{macro}{\p@check}
%    We check for any remaining replacements. If there are none, we
%    may quit. "\toks@"~is the list of
%    remaining substitutions. "\endgroup"~stops and makes the
%    definition (check~"\^^a0" to~see~why), "\^^a1"~continues. By the
%    way, in case of an~error, we will later use~"\next@" in order to
%    tell what replacements were not carried out.
%    \begin{macrocode}
\def\p@check{\edef\next@{\the\toks@}%
        \ifx\empty\next@  \expandafter\endgroup
        \else  \expandafter\^^a1\fi}
%    \end{macrocode}
% \end{macro}
% \begin{macro}{\p@first}
%    This sets "\p@first" to the "\futuredef" expansion of the first
%    token we want to~match. "\^^a2"~will rewrap the rest of~"\toks@",
%    and needs an (as~to~yet) unmatched closing brace for that.
%    It~will provide the matching open one by~itself.
%    \begin{macrocode}
\def\^^a1{\iffalse{\fi
       \expandafter\futuredef \expandafter\p@first
       \expandafter\^^a2\the\toks@}}
%    \end{macrocode}
% \end{macro}
% Ok, we rewrap the rest to be matched into~"\p@match", and the
% replacement into~"\p@replace", after which we continue with~"\^^a3".
%    \begin{macrocode}
\def\^^a2#1#{\p@match{#1}\afterassignment\^^a3\p@replace}
%    \end{macrocode}
% The remaining substitutions we repack into~"\toks@". Now we need to
% insert the matching opening brace for the closing one we put~before.
%    \begin{macrocode}
\def\^^a3{\afterassignment\^^a4\toks@\expandafter{\iffalse}\fi}
%    \end{macrocode}
% We now get the first (or next) token of the original macro.
%    \begin{macrocode}
\def\^^a4{\futuredef\next\^^a5}
%    \end{macrocode}
% If this token matches~"\p@first", we check the rest in~"\^^a6". We
% collect in~"\toks@" all tokens matched so far (excluding "\p@first"),
% so that we can
% reinsert them if the match cannot be completed successfully. This~is
% done in a~separate group. If~"\next" turns out to
% be~"\@ndp@tch", however,
% this is an~error indication. It~means that the end of patchable
% material was reached. We call then~"\^^e1", which quits in that
% case in a somewhat unusual (but relatively fast) way, reinserting
% the gotten~"\@ndp@tch".
%
% It does not do any harm that "\next" is contained in conditional
% context. Coming from~"\futuredef", it cannot be "\let" to an
% unmatched conditional, and will correctly be~skipped.
%    \begin{macrocode}
\def\^^a5{\ifx\next\p@first
             \begingroup \toks@{}\expandafter\^^a6%
          \else\ifx\next\@ndp@tch \^^e1\fi
            \next \expandafter \^^a4%
          \fi}
%    \end{macrocode}
% In case of an error, we give the original macro (which has not yet
% been patched). And at definition time, we will show how the macro
% looks like afterwards.
%    \begin{macrocode}
\def\^^e1{\let\^^a4\endgroup
          \newlinechar`\^^J
          \toks@\expandafter{\next@}%
          \errorcontextlines\m@ne
          \errhelp{I am ignoring inapplicable patches. Go on.}%
          \errmessage{When trying to patch
            \expandafter\string\^^e0, which was defined as^^J%
            \expandafter\meaning\^^e0^^J%
            the following patches remained inapplicable:^^J%
            \the\toks@^^J%
            I will show the results of the succeeded patches as soon^^J%
            as I can without further comment, so do not be surprised.}%
          \aftergroup\show \expandafter\aftergroup\^^e0%
}
%    \end{macrocode}
% Ok, we look whether there are any tokens remaining to be matched. If
% there are not, replacement can go~forth. In~that case, we end our
% local group, and go over to~"\^^ac". If~there are, we continue
% with~"\^^a7".
%    \begin{macrocode}
\def\^^a6{\edef\next{\the\p@match}%
         \ifx\next\empty \endgroup\expandafter\^^ac%
         \else \expandafter\^^a7\fi}
%    \end{macrocode}
% We get the next token to be matched into~"\next@" from~"\p@match".
% We~will have to adjust "\p@match" again with a token list
% reassignment. For this we need to insert an unmatched closing brace
% after its expansion, which will again be matched later.
%    \begin{macrocode}
\def\^^a7{\iffalse{\fi
          \expandafter\futuredef\expandafter\next@
          \expandafter\^^a8\the\p@match}}
%    \end{macrocode}
% Ok, here we gather the rest into~"\p@match" and~continue.
%    \begin{macrocode}
\def\^^a8{\afterassignment\^^a9\p@match\expandafter{\iffalse}\fi}
%    \end{macrocode}
% Now we get the next token from the original macro into~"\next".
%    \begin{macrocode}
\def\^^a9{\futuredef\next\^^aa}
%    \end{macrocode}
% In case of a match, we continue with~"\^^ab". Otherwise, if~we have
% reached the illegal end of~macro ("\next" set to~"\@ndp@tch"),
% we~stop.
% If~we have no match legally, we reinsert~"\p@first", continue
% scanning with~"\^^a4", reinserting everything matched with the help
% of the "\futuredef" generated "\aftergroup"-sequence in~"\toks@".
% This will hapen also if "\@ndp@tch" indicates something went
% haywire, because "\@ndp@tch" cannot be in a~match sequence (if you
% do not put it there, and you are not allowed to).
% this we do also in the case of error, as you can easily see.
%    \begin{macrocode}
\def\^^aa{\ifx\next@\next
              \expandafter\^^ab%
          \else \aftergroup\p@first
          \aftergroup\^^a4%
          \the\toks@\next\expandafter\endgroup\fi}
%    \end{macrocode}
% We now have to append the "\aftergroup" sequence of the next matched
% token in~"\next" to~"\toks@". After that, we can loop.
%    \begin{macrocode}
\def\^^ab{\toks@\expandafter\expandafter\expandafter{%
         \expandafter\the\expandafter\toks@\next}%
         \^^a6}
%    \end{macrocode}
% Ok, here follows the code if a~match {\em was\/} completed. We
% insert the tokens of~"\p@replace". We~have to scan "\p@replace"
% token by~token, so that implicit braces work like in the match
% code sequences. We do this until "\p@replace" is exhausted. Which we
% can detect by finding "\@ndp@tch".
%    \begin{macrocode}
\def\^^ac{\expandafter\^^ad\the\p@replace\@ndp@tch}
%    \end{macrocode}
% The following analysis loop is about as straight as it can get.
%    \begin{macrocode}
\def\^^ad{\futuredef\next\^^ae}
\def\^^ae{\ifx\next\@ndp@tch
              \expandafter\p@check
          \else
              \next \expandafter\^^ad%
          \fi}
%    \end{macrocode}
% We end here by giving the driver file for the documentation, which
% will typically be extracted using~"docstrip.sty".
%    \begin{macrocode}
%<+driver>\documentstyle[doc]{article}
%<+driver>    \EnableCrossrefs
%<+driver>%    \DisableCrossrefs
%<+driver>
%<+driver>    \CodelineIndex
%<+driver>\begin{document}
%<+driver>  \DocInput{patch.doc}
%<+driver>\end{document}
%    \end{macrocode}
%\Finale

${this.title}

Code Editor : patch.tex