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\ProvidesExplPackage{mkessler-powerset}{2022/01/30}{2.8.1}{Iterate over powerset of clist}



\ExplSyntaxOn

%%% Iterate over powerset of claist

\clist_new:N  \l_powerset_copied_clist
\seq_new:N    \l_powerset_saved_seq



\cs_generate_variant:Nn \clist_remove_all:Nn { N V }

% Pseudocode of this macro
% remove left  -> push on stack
% call recursive
% add left to 'extra'
% call recursive
% remove left from 'extra'
% add from stack to left

\cs_new:Npn \__powerset_clist_foreach_aux:Nn #1 #2 
{
  \clist_if_empty:NTF \l_powerset_copied_clist
    {
      #2
    }
    {
      \clist_get:NN \l_powerset_copied_clist \l_tmpa_tl
      \seq_push:NV  \l_powerset_saved_seq \l_tmpa_tl
      \clist_pop:NN \l_powerset_copied_clist { \l_tmpa_tl }

      \__powerset_clist_foreach_aux:Nn #1 {#2}
      
      \seq_get:NN \l_powerset_saved_seq \l_tmpa_tl
      \clist_put_left:NV #1 \l_tmpa_tl

      \__powerset_clist_foreach_aux:Nn #1 {#2}

      \seq_get:NN \l_powerset_saved_seq \l_tmpa_tl
      \clist_remove_all:NV #1 \l_tmpa_tl
      \clist_push:NV \l_powerset_copied_clist \l_tmpa_tl
      \seq_pop:NN \l_powerset_saved_seq \l_tmpa_tl
    }
}


% Usage:
% \clist_use_powerset:Nn {clist variable name}{code for each subset}
% This will execute #2 for each subset of the listname given as #1
% In #2, the name given as #1 can be used for the current subset
% After execution, the value of #1 is restored
\cs_new:Npn \powerset_clist_foreach:Nn #1 #2
{
  \clist_set_eq:NN \l_powerset_copied_clist #1
  \clist_clear:N #1
  \clist_remove_duplicates:N \l_powerset_copied_clist

  \__powerset_clist_foreach_aux:Nn #1 {#2}

  \clist_set_eq:NN #1 \l_powerset_copied_clist
}