% \iffalse meta-comment
%<*internal>
\iffalse
%</internal>
%<*readme>
Variations on the `\expandafter` TeX primitive
==============================================
* E-mail: blflatex@gmail.com
* Released under the LaTeX Project Public License v1.3c or later
  See http://www.latex-project.org/lppl.txt

The package defines `\multiexpand`, `\multiexpandafter`, `\MultiExpand`
and `\MultiExpandAfter`, replacing large chains of `\expandafter`.
These four commands take as an argument the number of expansion to be
done.  If eTeX is available, this number is evaluated using `\numexpr`.

Say we want to expand `\C` five times before `\A` and `\B` in `\A\B\C`.
The traditional approach would be to insert 31 `\expandafter` before
`\A` and the same number before `\B`.  With this package one can use
any of

    \expandafter\A\expandafter\B\romannumeral\multiexpand{5}\C

    \expandafter\A\romannumeral\multiexpandafter{5}\B\C

    \MultiExpandAfter{2}\A\MultiExpandAfter{5}\B\C

    \MultiExpandAfter{2}\A\MultiExpandAfter{2}\B\MultiExpand{5}\C

In one step of expansion (triggered by the `\expandafter`'s),
`\romannumeral\multiexpand{5}` expands the following token 5 times,
whereas `\romannumeral\multiexpandafter{5}` expands the token after
that 5 times.  The macros `\MultiExpandAfter` and `\MultiExpand`
take two steps of expansion, but do not require `\romannumeral`.
Another example is that in two steps of expansion,

    \MultiExpandAfter{2}\a\MultiExpandAfter{3}{%
      \MultiExpandAfter{9}\b\MultiExpandAfter{10}\c\d}

expands `\d` 10 times, then `\c` 7 times (9-2), then `\b` once (3-2).

The package can be built from the file `multiexpand.dtx' by running

    pdflatex multiexpand.dtx
    pdflatex multiexpand.dtx

%</readme>
%<*lvt>
 \input regression-test.tex\relax
 \START
 \LONGTYPEOUT{Author: Bruno Le Floch}
%<lvt002> \let\numexpr\relax
 \input multiexpand.sty\relax

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % Introduce commands that expand to each other, to count how many times
 % things were expanded.
 \OMIT
 \def\i{}
 \def\v{\i\i\i\i}
 \def\x{\i\i\i\i\v}
 \def\l{\i\i\i\i\v\x\x\x\x}
 \def\c{\i\i\i\i\v\x\x\x\x\l}
 \def\d{\i\i\i\i\v\x\x\x\x\l\c\c\c\c}
 \def\m{\i\i\i\i\v\x\x\x\x\l\c\c\c\c\d}
 \TIMO

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % We test |\MultiExpand|, which needs two expansions. In particular, we see
 % that the implementation is reasonably quick, and we get the $2345$-th
 % expansion of |\m\m\m\m|.
 % 4000-2345 = 1655 = mdclv
 \TEST{MultiExpand many times (vlcdm)}{%
   \toks0\expandafter\expandafter\expandafter{\MultiExpand{2345}\m\m\m\m}%
   \TYPE{\the\toks0.}%
 }

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % Test |\MultiExpandAfter|, two expansions to get the specified expansion.
 % The results indirectly show that expansions happen in the expected order.
 % 100 = c
 % 100-(27-2) = 75 = lxxv
 % 100-(14-2) = 88 = lxxxviii
 % 100-38 = 62 = lxii
 \TEST{MultiExpandAfter chain (c vxxl iiivxxxl iixl)}{%
   \toks0\expandafter\expandafter\expandafter{%
     \MultiExpandAfter{27}\c
     \MultiExpandAfter{14}\c
     \MultiExpandAfter{38}\c\c}%
   \TYPE{\the\toks0.}%
 }

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % Test the order of expansion.  The example was given in the original
 % question that led to writing this package.  For the record, this
 % package (at some point) used 32 |\expandafter| to do the expansion
 % in the right order, which was better than other approaches; however
 % this counting ignores the large overheads due to other primitives.
 \OMIT
 \def\a#1.{#1}
 \def\b#1:{#1.}
 \def\c#1,{#1:}
 \def\d{Hello world!,}
 \TIMO
 %
 \TEST{MultiExpandAfter order}{%
   \toks0\MultiExpandAfter{3}{%
     \MultiExpandAfter{3}\a
     \MultiExpandAfter{3}\b
     \MultiExpandAfter{1}\c
     \d}%
   \TYPE{\the\toks0}%
 }

 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % The other example from the same question (expanding seven tokens once
 % each in the reverse order) takes 74 \expandafter.
 \OMIT
 \def\b.{.b}    \def\c.{.c}    \def\d.{.d}
 \def\e.{.e}    \def\f.{.f}    \def\g.{.g}
 \TIMO
 %
 \TEST{MultiExpandAfter order (2)}{%
   \toks0\MultiExpandAfter{2}{%
     \MultiExpandAfter3\a    \MultiExpandAfter3\b
     \MultiExpandAfter3\c    \MultiExpandAfter3\d
     \MultiExpandAfter3\e    \MultiExpandAfter1\f\g.}%
   \TYPE{\the\toks0}%
 }

 \END
%</lvt>
%<*tlg>
This is a generated file for the l3build validation system.
Don't change this file in any respect.
Author: Bruno Le Floch
(multiexpand.sty)
============================================================
TEST 1: MultiExpand many times (vlcdm)
============================================================
\v \l \c \d \m .
============================================================
============================================================
TEST 2: MultiExpandAfter chain (c vxxl iiivxxxl iixl)
============================================================
\c \v \x \x \l \i \i \i \v \x \x \x \l \i \i \x \l .
============================================================
============================================================
TEST 3: MultiExpandAfter order
============================================================
Hello world!
============================================================
============================================================
TEST 4: MultiExpandAfter order (2)
============================================================
\a .bcdefg
============================================================
%</tlg>
%<*internal>
\fi
\def\nameofplainTeX{plain}
\ifx\fmtname\nameofplainTeX\else
  \expandafter\begingroup
\fi
%</internal>
%<*install>
\input docstrip.tex
\keepsilent
\askforoverwritefalse
\preamble
----------------------------------------------------------------
multiexpand --- trigger multiple expansions in one expansion step.
E-mail: blflatex@gmail.com
Released under the LaTeX Project Public License v1.3c or later
See http://www.latex-project.org/lppl.txt
----------------------------------------------------------------

\endpreamble
\postamble

Copyright (C) 2011-2017 by Bruno Le Floch <blflatex@gmail.com>

This work may be distributed and/or modified under the
conditions of the LaTeX Project Public License (LPPL), either
version 1.3c of this license or (at your option) any later
version.  The latest version of this license is in the file:

http://www.latex-project.org/lppl.txt

This work is "maintained" (as per LPPL maintenance status) by
Bruno Le Floch.

This work consists of the file  multiexpand.dtx
and the derived files           multiexpand.ins,
                                multiexpand.pdf and
                                multiexpand.sty.

\endpostamble
\usedir{tex/latex/multiexpand}
\generate{
  \file{\jobname.sty}{\from{\jobname.dtx}{package}}
}
%</install>
%<install>\endbatchfile
%<*internal>
\usedir{source/latex/multiexpand}
\generate{
  \file{\jobname.ins}{\from{\jobname.dtx}{install}}
  \file{\jobname 001.lvt}{\from{\jobname.dtx}{lvt}}
  \file{\jobname 002.lvt}{\from{\jobname.dtx}{lvt,lvt002}}
}
\nopreamble\nopostamble
\generate{
  \file{\jobname 001.tlg}{\from{\jobname.dtx}{tlg}}
  \file{\jobname 002.tlg}{\from{\jobname.dtx}{tlg}}
}
\usedir{doc/latex/multiexpand}
\generate{
  \file{README.md}{\from{\jobname.dtx}{readme}}
}

\ifx\fmtname\nameofplainTeX
  \expandafter\endbatchfile
\else
  \expandafter\endgroup
\fi
%</internal>
%<*driver>
\documentclass[12pt]{ltxdoc}
\usepackage[T1]{fontenc}
\usepackage{hologo}
\usepackage{multiexpand}
\usepackage[margin=4cm]{geometry}
\usepackage{hyperref}
\RecordChanges
\begin{document}
  \DocInput{multiexpand.dtx}
\end{document}
%</driver>
% \fi
%
% \CheckSum{126}
%
% \def\fileversion{v1.5} \def\filedate{2017/11/29}
%\title{\texttt{multiexpand}\\
%  Trigger multiple expansions \\ in one expansion step\thanks{This file
%    describes version \fileversion, last revised \filedate.}}
%\author{Bruno Le Floch\thanks{E-mail: blflatex@gmail.com}
%  \thanks{I have gathered ideas from various posts in the \texttt{\{TeX\}}
%    community at \url{http://tex.stackexchange.com}. Thanks to their authors.}}
%\date{Released \filedate}
%
%\maketitle
%
% \tableofcontents
% \changes{v1.0}{2011/02/15}{First version with documentation}
% \changes{v1.1}{2013/01/08}{Version submitted to CTAN}
% \changes{v1.2}{2013/01/09}{Use fewer expandafter for large arguments}
% \changes{v1.2}{2013/01/09}{Change ME prefix to multiexpand}
% \changes{v1.4}{2015/09/20}{Clarify that eTeX is not required}
% \changes{v1.5}{2017/11/29}{Updates due to l3build changes}
%
% \section{Two user commands}
%
% \begin{itemize}
% \item For $n>0$, expanding |\MultiExpand{|$n$|}\macro| twice gives
%   the $n$-th expansion of |\macro|.
% \item For $n>0$, expanding |\MultiExpandAfter{|$n$|}\macroA\macroB|
%   twice expands |\macroB| $n$ times before expanding |\macroA|.
% \end{itemize}
% Note that neither functions work for $n = 0$.
%
% These can typically be combined as
% \begin{verbatim}
% \MultiExpand{7}%
% \MultiExpandAfter{4}\a\MultiExpandAfter{7}\b%
% \MultiExpandAfter{3}\c\d
% \end{verbatim}
% which would expand |\d| $3$~times, then |\c| $5$~times ($2$~of the $7$~times
% were used to expand |\MultiExpandAfter{3}|), then |\b| twice ($4-2$), and
% finally |\a| five times ($7-2$). Note that all this happens in precisely
% \emph{two} steps of expansion.
%
% In some cases, one needs to achieve the same effect in \emph{one} step
% only.  For this, we use the first expansion of |\MultiExpand|, which
% is |\romannumeral| |\multiexpand|, or of |\MultiExpandAfter|, which is
% |\romannumeral| |\multiexpandafter|.  In detail, expanding |\romannumeral|
% |\multiexpand{|$n$|}| once expands the following token $n$ times, and
% similarly for |\romannumeral| |\multiexpandafter{|$n$|}|.
%
% These are especially useful when we want to expand several times a
% very specific token which is buried behind many others. For instance,
% expanding the following code once
% \begin{verbatim}
% \expandafter\macroA\expandafter\macroB
% \romannumeral\multiexpandafter{4}\macroC\macroD
% \end{verbatim}
% will expand |\macroD| $4$ times before the three other macros.
%
% Note: as we mentionned, this breaks for $n=0$. But in this case, consider
% using |\expandafter\empty|, or a variant thereof.
%
% \section{Implementation}
%\StopEventually{\PrintChanges\PrintIndex}
%    \begin{macrocode}
%<*package>
%    \end{macrocode}
%
% We work inside a group, to change the catcode of |@|. So we will only
% do |\gdef|s.  Note that this code can be read several times with no
% issue; no need to bother to check whether it was already read or not.
%    \begin{macrocode}
\begingroup
\catcode `\@=11
%    \end{macrocode}
%
% \subsection{Common to the \hologo{eTeX} and non-\hologo{eTeX} cases}
%
% For the ``lazy'', who do not want to use |\romannumeral|, we provide
% |\MultiExpand| and |\MultiExpandAfter|, simple shorthands.  A drawback
% is that they require two steps of expansion rather than only one.
%    \begin{macrocode}
\gdef \MultiExpand {\romannumeral \multiexpand }
\gdef \MultiExpandAfter {\romannumeral \multiexpandafter }
%    \end{macrocode}
%
% \subsection{Without \hologo{eTeX}'s \cs{numexpr}}
% \changes{v1.3}{2015/03/03}{Support TeX with no numexpr}
%
% No need for the usual |\begingroup\expandafter\endgroup| to prevent
% |\numexpr| from being set to |\relax|, because we are already in a
% group.
%    \begin{macrocode}
\expandafter \ifx \csname numexpr\endcsname \relax
%    \end{macrocode}
%
% A helper.
%    \begin{macrocode}
\long \gdef \multiexpand@gobble #1{}
%    \end{macrocode}
%
% The user commands |\multiexpand| and |\multiexpandafter|, to be used
% after |\romannumeral|.  They only differ a little bit.
%    \begin{macrocode}
\gdef \multiexpand {\multiexpand@aux \multiexpand@ }
\gdef \multiexpandafter {\multiexpand@aux \multiexpand@after }
%    \end{macrocode}
% The user commands receives a number, and to accept various forms of
% numbers we hit it with |\number|.  If it is non-positive, stop the
% |\romannumeral| expansion with |0| and a space.  Otherwise, reverse
% the number, to make it easy to subtract~$1$.
%    \begin{macrocode}
\long \gdef \multiexpand@aux #1#2%
  {\expandafter \multiexpand@test \number #2;#1}
\gdef \multiexpand@test #1;#2%
  {%
    \ifnum #1>0
      \multiexpand@reverse #1{?\multiexpand@reverse@end }?;;#2%
    \fi
    0 %
  }
%    \end{macrocode}
% The macro |\multiexpand@reverse| puts characters from the number one
% by one (as~|#1|) after the semicolon, to reverse the number.  After
% the last digit, |#1| is |{?\multiexpand@reverse@end}|.  The question
% mark is removed by |\multiexpand@gobble|, and the |reverse@end|
% macro cleans up.  In particular, one should not forget to close the
% conditional using~|#5|, which is the trailing~|\fi|.  At this stage,
% |#4| is the function that distinguishes |\multiexpand| from
% |\multiexpand@after|, and |#3| is the reversed
% number.  \begin{macrocode}
\gdef \multiexpand@reverse #1#2;%
  {\multiexpand@gobble #1\multiexpand@reverse #2;#1}
\gdef \multiexpand@reverse@end #1;?#2#3;#4#50
  {#5\multiexpand@iterate #41#3;}
%    \end{macrocode}
% The macro |\multiexpand@iterate| applies a \meta{function} a certain
% number of times to what follows in the input stream.  It expects to
% receive \meta{function} \meta{nines} |1|\meta{reversed number}|;|.
% The argument \meta{nines}, made entirely of the digit~|9|, is used to
% compute carries when subtracting~$1$, and is initally empty.  As a
% concrete example, after |\multiexpand{302}| the successive
% calls to |\multiexpand@iterate| would go as follows.
% \begin{verbatim}
%   \multiexpand@iterate \multiexpand@  1203;
%   \multiexpand@iterate \multiexpand@  1103;
%   \multiexpand@iterate \multiexpand@  1003;
%   \multiexpand@iterate \multiexpand@ 9 103;
%   \multiexpand@iterate \multiexpand@ 99 13;
%   \multiexpand@iterate \multiexpand@  1992;
%   \multiexpand@iterate \multiexpand@  1892;
%   \multiexpand@iterate \multiexpand@  1792;
% \end{verbatim}
% Note in particular how carries are done in several steps.  The details
% are left as an exercise to the reader.  The most common case is when
% |#2| is empty and |#3| is a non-zero digit.  Then |\number| is
% expanded, triggering |\ifcase| which shifts |#3| by one unit, and |#1|
% takes care of expanding the tokens are required by |\multiexpand| or
% |\multiexpandafter|.  If |#3| is~$0$, then |\multiexpand@zero| is
% called, closing the conditional with |#1|, and iterating, this time
% with a non-empty \meta{nines}, which are the argument |#2| of a new
% call to |\multiexpand@iterate|.  Those \meta{nines} are put back into
% the number by |\multiexpand@iterate|, unless the next significant
% digit is also $0$, in which case |\multiexpand@zero| is called again,
% until finding a non-zero digit; at each step, one more $9$ is added to
% the \meta{nines}.  If all digits are zero, we reach |;| this way, and
% end, after cleaning up.
%    \begin{macrocode}
\gdef \multiexpand@iterate #1#21#3%
  {%
    \ifx ;#3\multiexpand@end \fi
    \ifx 0#3\multiexpand@zero \fi
    \expandafter \multiexpand@iterate
    \expandafter #1%
    \number 1#2%
      \ifcase #3 \or 0\or 1\or 2\or 3\or 4\or 5\or 6\or 7\or 8\fi
      #1%
  }
\gdef \multiexpand@zero #1#2\number 1#3\ifcase #4\fi #5%
  {#1\multiexpand@iterate #59#31}
\gdef \multiexpand@end #1#2\ifcase #3\fi #4{#10 }
%    \end{macrocode}
% Finally, the two different expansion commands.
%    \begin{macrocode}
\gdef \multiexpand@ #1;{#1\expandafter ;}
\gdef \multiexpand@after #1;{#1\expandafter ;\expandafter }
%    \end{macrocode}
%
% \subsection{With \hologo{eTeX}}
%
%    \begin{macrocode}
\else
%    \end{macrocode}
%
% With \hologo{eTeX}, everything is much easier, since the engine knows
% how to subtract~$1$.
%
% The main looping macros expect their arguments as an integer followed
% by a semicolon.  As long as the argument is at least~$2$, decrement
% it, and expand what follows.  Once the argument is~$1$ (or less: the
% macros are not meant to handle that case), call |\multiexpand@end| to clean up
% and stop looping.
%    \begin{macrocode}
\gdef \multiexpand@ #1;%
  {%
    \ifnum #1<2 \multiexpand@end \fi
    \expandafter \multiexpand@
    \the \numexpr #1-1\expandafter ;%
  }
\gdef \multiexpand@after #1;%
  {%
    \ifnum #1<2 \multiexpand@end \fi
    \expandafter \multiexpand@after
    \the \numexpr #1-1\expandafter ;\expandafter
  }
%    \end{macrocode}
% The looping macros are used within an overarching |\romannumeral|
% expansion, which we end with a |0| and a space, as well as the
% appropriate |\expandafter|.  Here, |#1| is |\fi| which needs to remain
% to close the conditional, |#2| is |\expandafter|, and there is a
% trailing |\expandafter| in the case of |\multiexpand@after|.
%    \begin{macrocode}
\gdef \multiexpand@end #1#2#3;{#10#2 }
%    \end{macrocode}
% Finally, user commands, used as |\romannumeral| |\multiexpand(after)|.
% Those evaluate their argument, and pass it to |\multiexpand@(after)|.
% The argument might contain |\par| tokens (who knows)
%    \begin{macrocode}
\long \gdef \multiexpand #1%
  {\expandafter \multiexpand@ \the \numexpr #1;}
\long \gdef \multiexpandafter #1%
  {\expandafter \multiexpand@after \the \numexpr #1;}
%    \end{macrocode}
%
%    \begin{macrocode}
\fi
%    \end{macrocode}
%
% Close the group.
%    \begin{macrocode}
\endgroup
%    \end{macrocode}
%
%    \begin{macrocode}
%</package>
%    \end{macrocode}
%\Finale
\endinput