pkgloader.sty

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \iffalse %%%%
%                                                                              %
%  Copyright (c) 2018 - Michiel Helvensteijn   (www.mhelvens.net)              %
%                                                                              %
%  https://github.com/mhelvens/latex-pkgloader                                 %
%                                                                              %
%  This work may be distributed and/or modified under the conditions           %
%  of the LaTeX Project Public License, either version 1.3 of this             %
%  license or (at your option) any later version. The latest version           %
%  of this license is in       http://www.latex-project.org/lppl.txt           %
%  and version 1.3 or later is part of all distributions of LaTeX              %
%  version 2005/12/01 or later.                                                %
%                                                                              %
%  This work has the LPPL maintenance status `maintained'.                     %
%                                                                              %
%  The Current Maintainer of this work is Michiel Helvensteijn.                %
%                                                                              %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \fi %%%%

% \CheckSum{0}
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% \subsection{Package Info}                                                    %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  First, the mandatory package meta-information:
%  
%    \begin{macrocode}
\NeedsTeXFormat{LaTeX2e}
\RequirePackage{expl3}
\ProvidesExplPackage{pkgloader}{2018/04/29}{0.7.0}
  {managing the options and loading order of LaTeX packages}
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% \subsection{Required Packages}                                               %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  The following packages are required. Two standard |expl3|-related
%  packages, one experimental package in |l3regex| and one user-contributed
%  |expl3| package in |lt3graph|:
%  
%    \begin{macrocode}
\RequirePackage{xparse}
\RequirePackage{l3keys2e}
\RequirePackage{l3regex}
\RequirePackage{lt3graph}
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% \subsection{Package Code}                                                    %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  We need two global data-structures. One to keep track of all packages
%  that are known, one to keep track of the packages that are actually
%  going to be loaded, and their order:
%  
%    \begin{macrocode}
\prop_new:N  \g__pkgloader_known_pkg_prop
\graph_new:N \g__pkgloader_pkg_graph
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  We store pristine versions of the three package loading
%  commands: 
%  
%    \begin{macrocode}
\cs_gset_eq:NN \__pkgloader_usepkg:wnw          \usepackage
\cs_gset_eq:NN \__pkgloader_RPkg:wnw            \RequirePackage
\cs_gset_eq:NN \__pkgloader_RPkgWithOptions:wnw \RequirePackageWithOptions
\cs_gset_eq:NN \__pkgloader_doccls:wnw          \documentclass
\cs_gset_eq:NN \__pkgloader_LCls:wnw            \LoadClass
\cs_gset_eq:NN \__pkgloader_LClsWithOptions:wnw \LoadClassWithOptions
%    \end{macrocode}
%  
%  And we define a command to clean up any and all commands
%  that we change or introduce. It will be called when they
%  are not needed anymore:
%  
%    \begin{macrocode}
\tl_new:N \__pkgloader_cleanup_commands:
\tl_put_right:Nn \__pkgloader_cleanup_commands: {
  \cs_gset_eq:NN \usepackage                \__pkgloader_usepkg:wnw
  \cs_gset_eq:NN \RequirePackage            \__pkgloader_RPkg:wnw
  \cs_gset_eq:NN \RequirePackageWithOptions \__pkgloader_RPkgWithOptions:wnw
  \cs_gset_eq:NN \documentclass             \__pkgloader_doccls:wnw
  \cs_gset_eq:NN \LoadClass                 \__pkgloader_LCls:wnw
  \cs_gset_eq:NN \LoadClassWithOptions      \__pkgloader_LClsWithOptions:wnw
}
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  This function globally registers a package loading rule,
%  which can be created with either the |\Load| command or
%  any of the hijacked |\usepackage|-like commands:
%  
%    \begin{macrocode}
\cs_new_protected:Nn \__pkgloader_register_rule:nnnnnnnnn {
  % #1: package or class name
  % #2: options
  % #3: version
  % #4: condition
  % #5: compiled condition
  % #6: packages to load before this one
  % #7: packages to load after  this one
  % #8: reason
  % #9: command
%    \end{macrocode}
%  
%  If this package or class hasn't been seen before,
%  register it and create a rule-counter for it:
%  
%    \begin{macrocode}
  \prop_if_in:NnF \g__pkgloader_known_pkg_prop {#1} {
    \prop_gput:Nnn \g__pkgloader_known_pkg_prop {#1} {}
    \int_new:c {g__pkgloader_count_(#1)_int}
  }
%    \end{macrocode}
%  
%  Increment the rule-counter:
%  
%    \begin{macrocode}
  \int_incr:c {g__pkgloader_count_(#1)_int}
%    \end{macrocode}
%  
%  Then, we set all properties of the 
%  
%    \begin{macrocode}
  \tl_set:Nf \l_tmpa_tl {\int_use:c {g__pkgloader_count_(#1)_int}}
  \tl_set:cn  {g__pkgloader_options_           (#1)_(\l_tmpa_tl)_tl} {#2}
  \tl_set:cn  {g__pkgloader_version_           (#1)_(\l_tmpa_tl)_tl} {#3}
  \tl_set:cn  {g__pkgloader_condition_         (#1)_(\l_tmpa_tl)_tl} {#4}
  \tl_set:cn  {g__pkgloader_compiled_condition_(#1)_(\l_tmpa_tl)_tl} {#5}
  \tl_set:cn  {g__pkgloader_predecessors_      (#1)_(\l_tmpa_tl)_tl} {#6}
  \tl_set:cn  {g__pkgloader_successors_        (#1)_(\l_tmpa_tl)_tl} {#7}
  \tl_set:cn  {g__pkgloader_reason_            (#1)_(\l_tmpa_tl)_tl} {#8}
  \tl_set:cn  {g__pkgloader_command_           (#1)_(\l_tmpa_tl)_tl} {#9}
  \bool_new:c {g__pkgloader_used_              (#1)_(\l_tmpa_tl)_bool}
%    \end{macrocode}
%    \uninteresting\begin{macrocode}
}
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  These six macros are redefined to just register
%  the loading information rather than load the
%  package or class immediately. The distinction between
%  package and class is made by prefixing the name
%  with either |.sty| or |.cls| (which will be stripped
%  off before the file is actually loaded):
%  
%    \begin{macrocode}
\RenewDocumentCommand {\usepackage} { o m o }
  { \__pkgloader_usepackage_cmd:nnnnnn
        {\usepackage} {#1} {#2.sty} {#3}
        {pkgloader-cls-pkg.sty} {} }
\RenewDocumentCommand {\RequirePackage} { o m o }
  { \__pkgloader_usepackage_cmd:nnnnnn
        {\RequirePackage} {#1} {#2.sty} {#3}
        {} {} }
\RenewDocumentCommand {\RequirePackageWithOptions} { o m o }
  { \__pkgloader_usepackage_cmd:nnnnnn
        {\RequirePackageWithOptions} {#1} {#2.sty} {#3}
        {} {} }
\RenewDocumentCommand {\documentclass} { o m o }
  { \__pkgloader_usepackage_cmd:nnnnnn
        {\documentclass} {#1} {#2.cls} {#3}
        {} {pkgloader-cls-pkg.sty} }
\RenewDocumentCommand {\LoadClass} { o m o }
  { \__pkgloader_usepackage_cmd:nnnnnn
        {\LoadClass} {#1} {#2.cls} {#3}
        {} {pkgloader-cls-pkg.sty} }
\RenewDocumentCommand {\LoadClassWithOptions} { o m o }
  { \__pkgloader_usepackage_cmd:nnnnnn
        {\LoadClassWithOptions} {#1} {#2.cls} {#3}
        {} {pkgloader-cls-pkg.sty} }
%    \end{macrocode}
%  
%  Storing this information is delegated to the
%  |\__pkgloader_register_rule:nnnnnnnnn| function:
%  
%    \begin{macrocode}
\cs_new:Nn \__pkgloader_usepackage_cmd:nnnnnn {
  \__pkgloader_register_rule:nnnnnnnnn
    {#3} {#2} {#4}                  % package name, options, version
    {pkgloader-true.sty}            % condition
    {\c_true_bool}                  % compiled condition
    {#5} {#6}                       % predecessors, successors
    {it~is~requested~by~the~author} % reason
    {#1}                            % command
}
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  This is a sophisticated user-level command for manipulating
%  package loading order and conditions. It has a `non-standard'
%  but convenient syntax, which scans for clauses rather than
%  taking standard parameters:
%  
%    \begin{macrocode}
\NewDocumentCommand {\Load} {} {
%    \end{macrocode}
%  
%  Initialize the variables used for storing given data:
%  
%    \begin{macrocode}
  \tl_clear:N       \l__pkgloader_load_extension_tl
  \tl_clear:N       \l__pkgloader_load_options_tl
  \tl_clear:N       \l__pkgloader_load_name_tl
  \tl_clear:N       \l__pkgloader_load_version_tl
  \clist_clear:N    \l__pkgloader_load_pred_clist
  \clist_clear:N    \l__pkgloader_load_succ_clist
  \tl_clear:N       \l__pkgloader_load_cond_tl
  \tl_clear:N       \l__pkgloader_load_because_tl
  \tl_clear:N       \l__pkgloader_load_cmd_tl
  \bool_set_false:N \l__pkgloader_early_late_used_bool
%    \end{macrocode}
%  
%  Start scanning for input:
%  
%    \begin{macrocode}
  \__pkgloader_load_scan_ext_:w
%    \end{macrocode}
%    \uninteresting\begin{macrocode}
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This function checks if the |class| keyword is given.
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_ext_:w {
  \peek_charcode_remove_ignore_spaces:NTF c {% % % class
    \__pkgloader_load_scan_ext_c:w
  }{ % % % % % % % % % % % % % % % % % % % % % % % package details
    \tl_set:Nn \l__pkgloader_load_extension_tl {.sty}
    \tl_set:Nn \l__pkgloader_load_cmd_tl {\RequirePackage}
    \__pkgloader_load_scan_pkg_:w
  }
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  The |class| keyword indicates that this is a document
%  class loading rule, rather than a package loading rule.
%  We record this and then goes on to scan the details:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_ext_c:w lass {
  \tl_set:Nn \l__pkgloader_load_extension_tl {.cls}
  \tl_set:Nn \l__pkgloader_load_cmd_tl {\LoadClass}
  \clist_put_right:Nn \l__pkgloader_load_succ_clist {pkgloader-cls-pkg.sty}
  \__pkgloader_load_scan_pkg_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  The following function starts scanning for the name of the package
%  central to this rule, as well as the options and minimum
%  version proposed for it. It also checks if the |error|
%  keyword is given.
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_pkg_:w {
  \peek_charcode_remove_ignore_spaces:NTF e {% % % error
    \__pkgloader_load_scan_pkg_e:w
  }{\peek_charcode_remove_ignore_spaces:NTF [ {% % package options
    \__pkgloader_load_scan_pkg_options:nw
  }{ % % % % % % % % % % % % % % % % % % % % % % % package name
    \__pkgloader_load_scan_pkg_:nw
  }}
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  The |error| keyword can take the place of a package name,
%  options and version. It is shorthand for the |pkgloader-error|
%  file, and then jumps ahead to scanning clauses:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_pkg_e:w rror {
  \tl_set:Nn \l__pkgloader_load_name_tl {pkgloader-error.sty}
  \__pkgloader_load_scan_clause_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This scans the options and goes ahead to scan the package name:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_pkg_options:nw #1 ] {
  \tl_set:Nn \l__pkgloader_load_options_tl {#1}
  \__pkgloader_load_scan_pkg_:nw
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This scans the package name (and adds the proper extension),
%  peeks ahead for a minimum version, and otherwise goes on to
%  scanning for clauses:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_pkg_:nw #1 {
  \tl_set:Nn \l__pkgloader_load_name_tl {#1}
  \tl_put_right:NV
      \l__pkgloader_load_name_tl
      \l__pkgloader_load_extension_tl
  \peek_charcode_remove_ignore_spaces:NTF [ {% % % % package version
    \__pkgloader_load_scan_version:nw
  }{ % % % % % % % % % % % % % % % % % % % % % % % % clauses
    \__pkgloader_load_scan_clause_:w
  }
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This scans the version, and then goes ahead to scan for clauses:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_version:nw #1 ] {
  \tl_set:Nn \l__pkgloader_load_version_tl {#1}
  \__pkgloader_load_scan_clause_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This is the start- and return-point used to scan
%  for (additional) |\Load| clauses:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_clause_:w {
  \peek_charcode_remove_ignore_spaces:NTF a {
    \peek_charcode_remove:NTF l { % % % % % % % % % always
      \__pkgloader_load_scan_clause_al:w
    }{\peek_charcode_remove:NTF f { % % % % % % % % after
      \__pkgloader_load_scan_clause_af:w
    }{
      \__pkgloader_load_end: a
    }}
  }{\peek_charcode_remove_ignore_spaces:NTF b { % 
    \peek_charcode_remove:NTF e {
      \peek_charcode_remove:NTF c { % % % % % % % because
        \__pkgloader_load_scan_clause_bec:w
      }{\peek_charcode_remove:NTF f { % % % % % % before
        \__pkgloader_load_scan_clause_bef:w
      }{
        \__pkgloader_load_end: be
      }}
    }{
      \__pkgloader_load_end: b
    }
  }{\peek_charcode_remove_ignore_spaces:NTF e { % % % early
    \__pkgloader_load_scan_clause_e:w
  }{\peek_charcode_remove_ignore_spaces:NTF i { % % % if
    \__pkgloader_load_scan_clause_i:w
  }{\peek_charcode_remove_ignore_spaces:NTF l { % % % late
    \__pkgloader_load_scan_clause_l:w
  }{
    \__pkgloader_load_end:
  }}}}}
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This processes the ``|always|'' clause, which loads this
%  package conditional on the ``|pkgloader-true|'' package being
%  loaded (which always is):
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_clause_al:w ways {
  \tl_put_right:Nn \l__pkgloader_load_cond_tl {~||~pkgloader-true}
  \__pkgloader_load_scan_clause_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This processes the ``|after|'' clause:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_clause_af:w ter #1 {
  \clist_map_inline:nn {#1} {
    \clist_put_right:Nn \l__pkgloader_load_pred_clist {##1.sty}
  }
  \__pkgloader_load_scan_clause_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This processes the ``|because|'' clause:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_clause_bec:w ause #1 {
  \tl_set:Nn \l__pkgloader_load_because_tl {#1}
  \__pkgloader_load_scan_clause_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This processes the ``|before|'' clause:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_clause_bef:w ore #1 {
  \clist_map_inline:nn {#1} {
    \clist_put_right:Nn \l__pkgloader_load_succ_clist {##1.sty}
  }
  \__pkgloader_load_scan_clause_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This processes the ``|early|'' clause, which orders
%  this package before the ``|pkgloader-early|'' stub:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_clause_e:w arly {
  \bool_set_true:N \l__pkgloader_early_late_used_bool
  \clist_put_right:Nn \l__pkgloader_load_succ_clist {pkgloader-early.sty}
  \__pkgloader_load_scan_clause_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This processes the ``|if|'' clause, which may still be
%  a manual condition or the ``|loaded|'' keyword:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_clause_i:w f {
  \peek_charcode_remove_ignore_spaces:NTF l {
    \__pkgloader_load_scan_clause_if_l:w
  }{
    \__pkgloader_load_scan_clause_if_:nw
  }
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This processes the ``|if loaded|'' clause, which uses
%  this package being loaded as the condition for the rule being used:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_clause_if_l:w oaded {
  \tl_put_right:Nn \l__pkgloader_load_cond_tl {~||~}
  \tl_put_right:NV \l__pkgloader_load_cond_tl \l__pkgloader_load_name_tl
  \__pkgloader_load_scan_clause_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This processes the ``|if|'' clause with a manual condition:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_clause_if_:nw #1 {
  \tl_put_right:Nn \l__pkgloader_load_cond_tl {~||~#1}
  \__pkgloader_load_scan_clause_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%
%  
%  This processes the ``|late|'' clause, which orders
%  this package after the ``|pkgloader-late|'' stub:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Npn \__pkgloader_load_scan_clause_l:w ate {
  \bool_set_true:N \l__pkgloader_early_late_used_bool
  \clist_put_right:Nn \l__pkgloader_load_pred_clist {pkgloader-late.sty}
  \__pkgloader_load_scan_clause_:w
}
%    \end{macrocode}
%  
%  %%%%%%%%%  %%%%%%%%%  %%%%%%%%%  %%%%%%%%%  %%%%%%%%%  %%%%%%%%%
%  
%  This function processes the collected data and registers it:
%  
%    \begin{macrocode}
\cs_new_protected_nopar:Nn \__pkgloader_load_end: {
%    \end{macrocode}
%  
%  We remove the leading ``\texttt{\ \textbar\textbar\ }'' from the condition:
%  
%    \begin{macrocode}
  \tl_remove_once:Nn \l__pkgloader_load_cond_tl {~||~}
%    \end{macrocode}
%  
%  If no condition is given at all, the default is: ``|if loaded|''
%  
%    \begin{macrocode}
  \tl_if_empty:NT \l__pkgloader_load_cond_tl
    { \tl_set_eq:NN \l__pkgloader_load_cond_tl \l__pkgloader_load_name_tl }
%    \end{macrocode}
%  
%  We now take the condition and compile it to a |\bool_if:|
%  kind of syntax. The original syntax is preserved to use in
%  error messages and such:
%  
%    \begin{macrocode}
  \tl_set_eq:NN \l__pkgloader_load_compd_cond_tl \l__pkgloader_load_cond_tl
  \regex_replace_all:nnN
    { [^\&\|\(\)\!\s]+ }
    { (\c{graph_if_vertex_exist_p:Nn}
       \c{g__pkgloader_pkg_graph}\cB\{\0\.sty\cE\}) }
    \l__pkgloader_load_compd_cond_tl
%    \end{macrocode}
%  
%  If no reason was given for this rule, it was obviously
%  `because of reasons':
%  
%    \begin{macrocode}
  \tl_if_empty:NT \l__pkgloader_load_because_tl
    { \tl_set:Nn \l__pkgloader_load_because_tl {of~reasons} }
%    \end{macrocode}
%  
%  Having gathered and processed the data, the rule is
%  registered:
%  
%    \begin{macrocode}
  \__pkgloader_register_rule:VVVVVVVVV
    \l__pkgloader_load_name_tl
    \l__pkgloader_load_options_tl
    \l__pkgloader_load_version_tl
    \l__pkgloader_load_cond_tl
    \l__pkgloader_load_compd_cond_tl
    \l__pkgloader_load_pred_clist
    \l__pkgloader_load_succ_clist
    \l__pkgloader_load_because_tl
    \l__pkgloader_load_cmd_tl
%    \end{macrocode}
%    \uninteresting\begin{macrocode}
}
\cs_generate_variant:Nn \tl_if_eq:nnF                        {VnF}
\cs_generate_variant:Nn \graph_gput_vertex:Nn                {NV}
\cs_generate_variant:Nn \graph_gput_edge:Nnn                 {NnV,NVn}
\cs_generate_variant:Nn \seq_gput_right:Nn                   {NV}
\cs_generate_variant:Nn \__pkgloader_register_rule:nnnnnnnnn {VVVVVVVVV}
\tl_new:N    \l__pkgloader_load_extension_tl
\tl_new:N    \l__pkgloader_load_options_tl
\tl_new:N    \l__pkgloader_load_name_tl
\tl_new:N    \l__pkgloader_load_version_tl
\clist_new:N \l__pkgloader_load_pred_clist
\clist_new:N \l__pkgloader_load_succ_clist
\tl_new:N    \l__pkgloader_load_cond_tl
\tl_new:N    \l__pkgloader_load_because_tl
\tl_new:N    \l__pkgloader_load_cmd_tl
\bool_new:N  \l__pkgloader_early_late_used_bool
%    \end{macrocode}
%  
%  %%%%%%%%%  %%%%%%%%%  %%%%%%%%%  %%%%%%%%%  %%%%%%%%%  %%%%%%%%%
%
%  And here's the instruction to clean up the
%  |\Load| command-name at the end:
%  
%    \begin{macrocode}
\tl_put_right:Nn \__pkgloader_cleanup_commands:
  { \cs_undefine:N \Load }
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  This function decides, based on all loaded rules and package
%  requests, which packages, options and versions end up being
%  loaded, and in which order.
%  
%    \begin{macrocode}
\cs_new_protected:Nn \__pkgloader_select_packages: {
%    \end{macrocode}
%  
%  We first set up a graph to record accepted orderings:
%  
%    \begin{macrocode}
  \graph_clear:N \l__pkgloader_order_graph
%    \end{macrocode}
%  
%  We then start a loop that runs at least once, then repeats
%  while additional package configurations are still being added
%  to the set. Eventually the loop reaches a fixed point and terminates.
%  
%    \begin{macrocode}
  \bool_do_while:Nn \l__pkgloader_selection_changed_bool {
    \bool_set_false:N \l__pkgloader_selection_changed_bool
%    \end{macrocode}
%  
%  Then first, for all possible package configurations (a nested
%  loop, but not doubly indented because it feels like one loop):
%  
%    \begin{macrocode}
    \prop_map_inline:Nn \g__pkgloader_known_pkg_prop {%%%%%%%%%%%%%%   ##1
    \int_step_inline:nncn {1} {1} {g__pkgloader_count_(##1)_int} {%% ####1
%    \end{macrocode}
%  
%  If the current configuration should be loaded but still
%  isn't selected (nested conditional; but again, not indented):
%  
%    \begin{macrocode}
      \bool_if:cF {g__pkgloader_used_(##1)_(####1)_bool} {
      \bool_if:vT {g__pkgloader_compiled_condition_(##1)_(####1)_tl} {
%    \end{macrocode}
%  
%  We mark the package configuration as being used:
%  
%    \begin{macrocode}
        \bool_set_true:c {g__pkgloader_used_(##1)_(####1)_bool}
%    \end{macrocode}
%  
%  We record the configuration in the main package graph, which maps
%  each package to a clist of selected configurations:
%  
%    \begin{macrocode}
        \graph_get_vertex:NnNTF \g__pkgloader_pkg_graph {##1}
                                \l__pkgloader_used_configs_tl {
          \tl_if_empty:NTF \l__pkgloader_used_configs_tl
            { \graph_gput_vertex:Nnf \g__pkgloader_pkg_graph {##1} {####1} }
            { \graph_gput_vertex:Nnf \g__pkgloader_pkg_graph {##1}
                                    {\l__pkgloader_used_configs_tl, ####1} }
        }   { \graph_gput_vertex:Nnf \g__pkgloader_pkg_graph {##1} {####1} }
%    \end{macrocode}
%  
%  In a separate graph, we record the associated (now activated)
%  package loading orders. We don't do this in the main graph,
%  because it may involve packages that are themselves not yet
%  selected. These edges are later filtered and added to the main graph:
%  
%    \begin{macrocode}
        \graph_put_vertex:Nn \l__pkgloader_order_graph {##1}
        \clist_map_inline:cn {g__pkgloader_predecessors_(##1)_(####1)_tl} {
          \graph_put_vertex:Nn \l__pkgloader_order_graph {########1}
          \graph_get_edge:NnnNTF \l__pkgloader_order_graph
                {########1} {##1} \l__pkgloader_used_configs_tl
            { \graph_put_edge:Nnnn \l__pkgloader_order_graph
                    {########1} {##1} {\l__pkgloader_used_configs_tl,####1} }
            { \graph_put_edge:Nnnn \l__pkgloader_order_graph
                    {########1} {##1}                               {####1} }
        }
        \clist_map_inline:cn {g__pkgloader_successors_(##1)_(####1)_tl} {
          \graph_put_vertex:Nn \l__pkgloader_order_graph {########1}
          \graph_get_edge:NnnNTF \l__pkgloader_order_graph
                {##1} {########1} \l__pkgloader_used_configs_tl
            { \graph_put_edge:Nnnn \l__pkgloader_order_graph
                    {##1} {########1} {\l__pkgloader_used_configs_tl,####1} }
            { \graph_put_edge:Nnnn \l__pkgloader_order_graph
                    {##1} {########1}                               {####1} }
        }
%    \end{macrocode}
%  
%  We then mark the change, so a next iteration will be entered:
%  
%    \begin{macrocode}
        \bool_set_true:N \l__pkgloader_selection_changed_bool
%    \end{macrocode}
%    \uninteresting\begin{macrocode}
      }}
    }}
  }
%    \end{macrocode}
%  
%  We put the applicable proposed orderings into the
%  graph of selected packages:
%  
%    \begin{macrocode}
  \graph_gput_edges_from:NN \g__pkgloader_pkg_graph \l__pkgloader_order_graph
%    \end{macrocode}
%  
%  If there is a cycle in the derived package loading order: ERROR
%  
%    \begin{macrocode}
  \graph_if_cyclic:NT \g__pkgloader_pkg_graph
    {  \msg_fatal:nn {pkgloader} {cyclic-order}  }
%    \end{macrocode}
%  
%  Finally, we apply some default orderings where needed:
%  \begin{itemize}
%    \item If a package should not specifically
%          go early or late, it goes inbetween; and
%    \item if a package should not specifically
%          go before a class, it goes after.
%  \end{itemize}
%  
%    \begin{macrocode}
  \graph_map_vertices_inline:Nn \g__pkgloader_pkg_graph {
    \seq_if_in:NnF \g__pkgloader_system_packages_seq {##1} {
      \graph_acyclic_if_path_exist:NnnF \g__pkgloader_pkg_graph
          {##1} {pkgloader-early.sty} {
        \graph_acyclic_if_path_exist:NnnF \g__pkgloader_pkg_graph
            {pkgloader-late.sty} {##1} {
          \graph_put_edge:Nnn \g__pkgloader_pkg_graph {pkgloader-early.sty} {##1}
          \graph_put_edge:Nnn \g__pkgloader_pkg_graph {##1} {pkgloader-late.sty}
      } }
      \graph_acyclic_if_path_exist:NnnF \g__pkgloader_pkg_graph
          {##1} {pkgloader-cls-pkg.sty} {
        \graph_put_edge:Nnn \g__pkgloader_pkg_graph {pkgloader-cls-pkg.sty} {##1}
  } } }
%    \end{macrocode}
%    \uninteresting\begin{macrocode}
}
\cs_generate_variant:Nn \int_step_inline:nnnn  {nncn}
\cs_generate_variant:Nn \bool_if:nT            {vT}
\cs_generate_variant:Nn \withargs:nnn          {vvn}
\cs_generate_variant:Nn \graph_gput_vertex:Nnn {Nnf}
\graph_new:N \l__pkgloader_order_graph
\tl_new:N    \l__pkgloader_used_configs_tl
\bool_new:N  \l__pkgloader_selection_changed_bool
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  Now follows the user command to consolidate all package
%  loading requests and do the `right thing' (tm). Invoking
%  this command ends the work of |pkgloader|.
%  
%    \begin{macrocode}
\NewDocumentCommand {\LoadPackagesNow} {} {
%    \end{macrocode}
%  
%  We first select package configurations by their loading conditions:
%  
%    \begin{macrocode}
  \__pkgloader_select_packages:
%    \end{macrocode}
%  
%  Now to clean up after |pkgloader|, restoring
%  and removing various command-names.
%  
%    \begin{macrocode}
  \__pkgloader_cleanup_commands:
%    \end{macrocode}
%  
%  Then, for all used packages, in topological order\ldots
%  
%    \begin{macrocode}
  \graph_map_topological_order_inline:Nn \g__pkgloader_pkg_graph {
%    \end{macrocode}
%  
%  \ldots load that package. Though note that this code is still quite
%  incomplete, because it loads the first viable configuration. It should:
%  \begin{enumerate}
%      \item  use the |WithOptions| version of the command
%             if necessary,
%      \item  allow custom merging schemes for options, and
%      \item  use the latest required version.
%  \end{enumerate}
%    \begin{macrocode}
    \withargs:xn { \clist_item:nn{##2}{1} } {
      \withargs:vvfvn {g__pkgloader_command_(##1)_(####1)_tl}
                      {g__pkgloader_options_(##1)_(####1)_tl}
                      {\__pkgloader_strip_extension:f{##1}}
                      {g__pkgloader_version_(##1)_(####1)_tl} {
        \IfValueTF {########2}
          { \IfValueTF {########4}
              { ########1 [########2] {########3} [########4] }
              { ########1 [########2] {########3}             } }
          { \IfValueTF {########4}
              { ########1             {########3} [########4] }
              { ########1             {########3}             } }
%    \end{macrocode}
%    \uninteresting\begin{macrocode}
      }
    }
  }
}
\cs_generate_variant:Nn \withargs:nn {xn}
\cs_generate_variant:Nn \withargs:nnnnn {vvfvn}
%    \end{macrocode}
%  
%  And it needs the following auxiliary function to strip
%  filenames from their four character extension:
%  
%    \begin{macrocode}
\cs_new:Npn \__pkgloader_strip_extension:f #1 {
  \tl_reverse:f{
    \tl_tail:f{\tl_tail:f{\tl_tail:f{\tl_tail:f{
      \tl_reverse:n{#1}
    }}}}
  }
}
\cs_generate_variant:Nn \tl_reverse:n {f}
%    \end{macrocode}
%  
%  It's a bit clunky. Is there a substring function
%  in |expl3| we could use that I don't know about?
%
%  And here's the instruction to clean up the
%  |\LoadPackagesNow| command-name at the end:
%  
%    \begin{macrocode}
\tl_put_right:Nn \__pkgloader_cleanup_commands:
  { \cs_undefine:N \LoadPackagesNow }
%    \end{macrocode}
%  
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  
%  
%    \begin{macrocode}
\cs_gset_eq:NN \__pkgloader_begin_env:n \begin
\RenewDocumentCommand {\begin} {m} {
  \tl_if_eq:nnT {#1} {document} {\LoadPackagesNow}
  \__pkgloader_begin_env:n {#1}
}
\tl_put_right:Nn \__pkgloader_cleanup_commands:
  { \cs_gset_eq:NN \begin \__pkgloader_begin_env:n }
%    \end{macrocode}
%  
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  Bootstrap |pkgloader| by inserting |pkgloader-true| in
%  the graph directly, so all other packages can be inserted
%  with rules, possibly using the |always| clause.
%  
%    \begin{macrocode}
\graph_gput_vertex:Nn \g__pkgloader_pkg_graph {pkgloader-true.sty}
%    \end{macrocode}
%  
%  We keep a list of all pkgloader dummy packages:
%  
%    \begin{macrocode}
\seq_new:N \g__pkgloader_system_packages_seq
\cs_generate_variant:Nn \seq_gset_from_clist:Nn {Nx}
\seq_gset_from_clist:Nx \g__pkgloader_system_packages_seq
  {\tl_to_str:n
     {pkgloader-true.sty,
      pkgloader-false.sty,
      pkgloader-early.sty,
      pkgloader-late.sty,
      pkgloader-cls-pkg.sty}}
%    \end{macrocode}
%  
%  We then register the core logical rules of |pkgloader|,
%  regarding fundamental package `stubs' like |pkgloader-false|,
%  |pkgloader-error|, |pkgloader-early|, and so on.
%  
%    \begin{macrocode}
\withargs:nn {of~the~mandatory~core~rules~of~pkgloader} {
  \Load error if {pkgloader-false}                because {#1}
  \Load {pkgloader-true}    always                because {#1}
  \Load {pkgloader-early}   always                because {#1}
  \Load {pkgloader-late}    always                because {#1}
  \Load {pkgloader-cls-pkg} always                because {#1}
  \Load {pkgloader-early} before {pkgloader-late} because {#1}
}
%    \end{macrocode}
%  
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%
%  We process the options passed to |pkgloader| as |.sty| files
%  to be loaded before pkgloader does its thing. This
%  should be used to define new |pkgloader| rules. Note,
%  particularly, that any |\usepackage|-like command inside
%  those |.sty| files is registered and processed by
%  |pkgloader|; not loaded directly. 
%
%  First, we define the functions used to handle an option.
%  
%    \begin{macrocode}
\cs_new:Nn \__pkgloader_process_option:n
  { \__pkgloader_process_option:nn {#1} {true} }
\cs_new:Nn \__pkgloader_process_option:nn
  { \tl_if_eq:nnTF {#2} {true}
        { \seq_put_right:Nn  \l__pkgloader_rule_packages_seq {#1} }
        { \seq_remove_all:Nn \l__pkgloader_rule_packages_seq {#1} } }
%    \end{macrocode}
%  
%  The |recommended| rules are loaded unless explicitly turned off.
%  
%    \begin{macrocode}
\seq_new:N \l__pkgloader_rule_packages_seq
\seq_put_right:Nn \l__pkgloader_rule_packages_seq {recommended}
%    \end{macrocode}
%  
%  Process the options to populate |\l__pkgloader_rule_packages_seq|.
%  
%    \begin{macrocode}
\cs_generate_variant:Nn \keyval_parse:NNn {NNv}
\keyval_parse:NNv
  \__pkgloader_process_option:n
  \__pkgloader_process_option:nn
  {opt@pkgloader.sty}
\seq_remove_duplicates:N \l__pkgloader_rule_packages_seq
%    \end{macrocode}
%  
%  Actually load the |.sty| files in |\l__pkgloader_rule_packages_seq|.
%  Note that the actual file needs the |pkgloader-| prefix.
%  
%    \begin{macrocode}
\seq_map_inline:Nn \l__pkgloader_rule_packages_seq
  { \__pkgloader_RPkg:wnw {pkgloader-#1} }
%    \end{macrocode}
%  
%  Finally, we make a show of using the proper macros for \LaTeX's
%  benefit. If we don't, a \LaTeX\ error is issued.
%  
%    \begin{macrocode}
\DeclareOption*{}
\ProcessOptions\relax
%    \end{macrocode}
%  
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%



%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%  
%  Finally, here are the error messages this package can generate.
%  First a simple error for cycles, which should be improved to
%  show the cause of the cycle.
%  
%    \begin{macrocode}
\msg_new:nnn {pkgloader} {cyclic-order}
  {  There~is~a~cycle~in~the~requested~package~loading~order.  }
%    \end{macrocode}
%  
%  And the following is the error reported for certain package
%  combinations that have been forbidden through an |error| rule.
%  
%    \begin{macrocode}
\msg_new:nnnn {pkgloader} {illegal-combination}
  {  A~combination~of~packages~fitting~the~following~condition~
     was~requested:
     \\\\\ \ \ \ #1\\\\
     This~is~an~error~because~#2.  }
  {  A~pkgloader~rule~was~requested~that~prohibits~the~logical~
     combination\\above~for~the~specified~reason.~It~is~probably~
     a~good~reason.  }
%    \end{macrocode}
%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%