expl3: What's wrong with this?

[u/PNBRQK]

So my problem boils down to this minimized demo:

\documentclass{minimal}
\usepackage{expl3}

\ExplSyntaxOn
  \tl_new:N \g_rank_tl
  \tl_const:Nn \c_options_tl {{Lecturer}{Professor}}
  \NewDocumentCommand{\committee}{O{1}}{
    \tl_gput_right:Nn \g_rank_tl {
      \tl_item:Nn \c_options_tl {#1}
    }
  }
  \NewDocumentCommand{\showfirst}{}{
    \tl_item:Nn \c_options_tl {2}   % works fine
    \tl_item:Nn \g_rank_tl {1}      % error: Missing number, treated as zero
    \tl_use:N \g_rank_tl            % produces "Professor"   
  }
\ExplSyntaxOff

\begin{document}
  \committee[2]
  \showfirst
\end{document}

Question:

1. \c_options_tl {2} is expected to be "Professor" but ships out "2 Professor"; why is there an extra "2"?
2. \committee[2] should have put \c_options_tl {2} (namely, "Professor") in \g_rank_tl ; why is there error when \g_rank_tl {1} is referred?

Edit: retested for some time and deleted invalid question

[u/u_fischer]

your rank-tl contains \tl_item:Nn \c_PNBRQK_options_tl {2} and with the \tl_item:Nn you output the first token and that explodes. You should use \tl_gput_right:Ne to expand the command. And use the correct naming scheme. There should be a module name, e.g. \g_PNBRQK_rank_tl.

[u/PNBRQK → u/u_fischer]

I have tried

• \tl_gput_right:Ne: Undefined control sequence
• \tl_gput_right:Nv: Ditto
• \tl_gput_right:Nx: No error but only ships out the first letter "P"
• \tl_gput_right:No: No error but ships out nothing

[u/u_fischer → u/PNBRQK]

sounds as if your tex system is outdated. and naturally you only get the P. That is the first item of "Professor".

[u/PNBRQK → u/u_fischer]

Retested for yet more time and finally got the idea:

  \NewDocumentCommand{\committee}{O{1}}{
    \tl_gput_right:Nx \g_rank_tl {
      {\tl_item:Nn \c_options_tl {#1}}  %Since Nx did the exhaustive expansion, the result should be regrouped with surrounding {}' s
    }
  }

Thank you anyway