timetravel.sty

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Use the command \setCounters{counter1,counter2,..} to specify the
%% set of counters that should be included in the time travel.
%%
%% Create named wormholes using the command \wormhole{name}.
%%
%% Between \begin{backInTime}{wormholename} and \end{backInTime}, the
%% counters specified with \setCounters are temporarily reset to the
%% value they had when the wormhole with the name "wormholename" was
%% defined.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\ProvidesPackage{timetravel}

\newcommand{\setCounters}[1]{
  \def\@allCounters{#1}
  \@initCounters
}

\newcommand{\wormhole}[1]{
  % the argument is a new label
  %
  % just save all counters at this point and associate the values with
  % the new label
  \@processlist{\@saveCounter{#1}}{\@allCounters}
}

\newenvironment{backInTime}[1]{
  % first argument is a label defined with \wormhole
  %
  % sets all counters back to the value they had when the label was
  % defined and restore the current value afterwards
  \@processlist{\begin{@tmpRestoreCounter}{#1}}{\@allCounters}
}{
  \@processlist{\end{@tmpRestoreCounter}\@comment}{\@allCounters}
}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% internal stuff
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% 

\def\@allCounters{}

\newcommand{\@saveCounter}[2]{
  % first argument is the label, second the counter
  %
  % just save the value of the counter at the current position
  \newcounter{#1#2}
  \setcounter{#1#2}{\value{#2}}
}

\newcommand{\@initCounters}{
  \@processlist{\@makeTmpCounter}{\@allCounters}
}

\newcommand{\@makeTmpCounter}[1]{
  \newcounter{tmp#1}
}

\newenvironment{@tmpRestoreCounter}[2]{
  % first argument is the label, second the counter
  %
  % sets the counter back to the value it had at the label defined
  % with \wormhole and restores the current value afterwards
  \def\counter{#2}
  % \newcounter{tmp#2}
  \setcounter{tmp#2}{\value{#2}}
  \setcounter{#2}{\value{#1#2}}
}{
  \setcounter{\counter}{\value{tmp\counter}}
}

\newcommand{\@comment}[1]{}


\newcommand{\@processlist}[2]{
  \@for\timetraveliter:=#2\do{%
    #1{\timetraveliter}
  }
}