LaTeX: Using TeX as a calculator

tccalc.tex

\documentclass{minimal}
\batchmode         % suppress terminal output
\usepackage{expl3}[2012/09/05]
\errorstopmode     % resume terminal output
\ExplSyntaxOn
%% calculator repl loop
\tl_new:N \l_tchcl_input_tl
\tl_new:N \l_tchcl_answer_tl
\bool_new:N \l_tchcl_quit_bool
\group_begin:
  \char_set_catcode_active:N \*
  \cs_gset:Nn \tchcl_readin:
    { 
      \ior_get_str:NN \c_term_ior *
      \tl_set_eq:NN \l_tchcl_input_tl *
    }
\group_end:
\bool_until_do:Nn \l_tchcl_quit_bool
  {
    \tchcl_readin:
    \tl_if_blank:VTF \l_tchcl_input_tl
      { \bool_set_true:N \l_tchcl_quit_bool }
      {
        \tl_set:Nf \l_tchcl_answer_tl { \fp_to_tl:n { \l_tchcl_input_tl } }
        \iow_term:x { -> \l_tchcl_answer_tl }
      }
  }
\ExplSyntaxOff
\stop   % quit immediately
\begin{document}
\end{document}