xparse-arglist.sty

\ProvidesPackage{xparse-arglist}
\RequirePackage{xparse}

% This package provides a way to define an xparse-based command which is
% "aware" of how it was called.  In other words, while executing the command,
% we construct the argument list that was used to call it (or at least
% something very close to, and functionally equivalent to this argument list).
% 
% To construct the argument list, we need to provide \ArgumentSpecification,
% either manually or by calling \GetDocumentCommandArgSpec (see xparse manual
% 3.4) and then expand \ArgumentList in the following way:
% 
% \ArgumentList must be first fully expanded both when defining the command,
% and the result must be then fully expanded while executing the command.
% 
% For example, to have \foo itself with the same arguments again :D define it
% like this:
% 
% \edef\outermarshal{%
%   \noexpand\NewDocumentCommand
%     \noexpand\foo
%     {\expandonce{\ArgumentSpecification}}%
%     {%
%       \unexpanded{...}%
%       \edef\noexpand\innermarshal{%
%         \noexpand\noexpand\noexpand\foo\ArgumentList
%       }\innermarshal
%       \noexpand\foo\ArgumentList
%       \unexpanded{...}%
%     }%
% }\outermarshal
%
% This package was implemented during the development of "memoize", which
% needs to compute the md5sum of a command plus its arguments, and then
% (sometimes) execute the command.
% 
% Now maybe this exists somewhere in xparse, but I haven't been able to find
% it. And I know I should've used expl3 for this ... but plain TeX way
% compiles faster. ;-)

\def\ArgumentList{%
  \expandafter\xp@arglist\expandafter0\ArgumentSpecification.%
}

\def\xp@arglist#1#2{%
  \ifcsname xp@arglist@#2\endcsname
    \csname xp@arglist@#2\expandafter\expandafter\expandafter\endcsname
  \else
    \expandafter\xp@arglist@error
  \fi
  \expandafter{\the\numexpr#1+1\relax}%
}

% \xp@arglist@...: #1 = the argument number
\def\xp@arglist@m#1{\noexpand\unexpanded{{#####1}}\xp@arglist{#1}}
\def\xp@arglist@r#1#2#3{\noexpand\unexpanded{#2#####1#3}\xp@arglist{#1}}
\def\xp@arglist@R#1#2#3#4{\noexpand\unexpanded{#2#####1#3}\xp@arglist{#1}}
\def\xp@arglist@v#1{{Handled commands with verbatim arguments are not
    supported}\xp@arglist{#1}} % error
\def\xp@arglist@b#1{{This is not the way to handle
    environment}\xp@arglist{#1}} % error
\def\xp@arglist@o#1{\noexpand\unexpanded{[#####1]}\xp@arglist{#1}}
\def\xp@arglist@d#1#2#3{\noexpand\unexpanded{#2#####1#3}\xp@arglist{#1}}
\def\xp@arglist@O#1#2{\noexpand\unexpanded{[#####1]}\xp@arglist{#1}}
\def\xp@arglist@D#1#2#3#4{\noexpand\unexpanded{#2#####1#3}\xp@arglist{#1}}
\def\xp@arglist@s#1{\noexpand\IfBooleanT{#####1}{*}\xp@arglist{#1}}
\def\xp@arglist@t#1#2{\noexpand\IfBooleanT{#####1}{#2}\xp@arglist{#1}}
\csdef{xp@arglist@+}#1{\expandafter\xp@arglist\expandafter{\the\numexpr#1-1\relax}}%
\csdef{xp@arglist@.}#1{}
% e,E: Embellishments are not supported.
% > Argument processors are not supported. And how could they be?
\def\xp@arglist@error#1.{{Unknown argument type}}