How to pass an argument to lua tex.print with maths

Question

I want to create a blank exercise, in which answers can be text or mathematical expression, and to have below a list of all answers in disorder.

In the MWE i made with LUA, the text appears below as expected, but I don't know how to have math expressions like $\pi$ or $\frac{2}{3}$.

Any help would be appreciated.

\documentclass{article}
\usepackage{xcolor}
\usepackage{luacode}
\setlength\parindent{0pt}
\directlua{list={}; }
\def\hide#1{
  \directlua{ table.insert(list,"#1") }
  \textcolor{red}{#1} % final version will have white instead of red
}
\begin{document}
Try with \hide{text}.\
Try with \hide{ LUA \directlua{ tex.sprint(math.pi); } }.\
Try with \hide{ \bf{command} }.\
Try with \hide{ "math mode $\pi$" }.\par\vspace{\baselineskip}
\rule[2ex]{\linewidth}{0.5pt}
\directlua{ for i,v in ipairs(list) do 
    tex.print(v);
    tex.print("\noexpand\\");
    end }
\end{document}

---

EDIT: I updated my code thanks to Mico, and i made the answers to appears in boxes. The problem comes when the hidden answer is a part of a math expression and surrounded with delimiters, like the last two exemples: perenthesis and curly braces of fraction.

The resulting errors both point to the end of last \luaexec block: "Missing $ inserted." and "Extra }, or forgotten $."

I wonder if there is any way to solve this. Here is the code:

\documentclass{article}
\usepackage{xcolor}
\usepackage{luacode} % for '\luastringN' and '\luaexec' macros
\setlength\parindent{0pt}
\renewcommand{\baselinestretch}{1.5}
\everymath{\displaystyle}
\directlua{list={}} % intialize a Lua table object
\def\hide#1{%
   \directlua{ table.insert(list,\luastringN{#1})}%
   \textcolor{red}{#1}% final version will have white instead of red
}
\begin{document}
Try with \hide{text}.\par
Try with \hide{LUA \directlua{ tex.sprint(math.pi)}}.\par
Try with \hide{\textbf{command}}.\par
Try with \hide{math mode $\pi$ inside}.\par
Try with inside math mode $\hide{\pi}$.\par
Try with inside math delimiters $f(x)=( \ \hide{5-x^2}\ ) e^x$.\par
Try with inside math delimiters $f(x)=\frac{ \hide{4-\sqrt{x}} }{e^x}$.\par
\vspace{\baselineskip}\hrule\vspace{\baselineskip}
\luaexec{
  for i,v in ipairs(list) do
      tex.sprint ( '\fbox{'..v..'} \ ' )
  end
}
\end{document}

Again, any help would be appreciated.

Answer 1

Combining the ideas of:

• \newcommand: How to determine if in math mode (and then include $ $)?
• Define a command differently in inline vs display mode

You can do something like this

% !TeX TS-program = lualatex
\documentclass{article}
\usepackage{xcolor}
\usepackage{expl3}
\usepackage{luacode} % for '\luastringN' and '\luaexec' macros
\usepackage{unicode-math}
\setlength\parindent{0pt}
\renewcommand{\baselinestretch}{1.5}
\everymath{\displaystyle}
\directlua{list={}} % intialize a Lua table object
% select version by using \finaltrue or \finalfalse
\newif\iffinal
%\finaltrue
\finalfalse
\ExplSyntaxOn
\cs_set:Npn \hide #1 {
    % check if in math mode
    \relax\ifmmode
        \directlua{ table.insert(list,\luastringN{$#1$})}
    \else
        % normal text mode
        \directlua{ table.insert(list,\luastringN{#1})}
    \fi
    % instead of making things white, we simply create a placeholder with the same dimensions
    % this prevents the learners from copying the answer from a PDF viewer
    \iffinal
        \phantom{#1}
    \else
        \textcolor{red}{#1}
    \fi
}
\ExplSyntaxOff
\begin{document}
Try with \hide{text}.\par
Try with \hide{LUA \directlua{ tex.sprint(math.pi)}}.\par
Try with \hide{\textbf{command}}.\par
Try with \hide{math mode $\pi$ inside}.\par
Try with inside math mode $\hide{\pi}$.\par
Try with inside math delimiters $f(x)=( \ \hide{5-x^2}\ ) e^x$.\par
Try with inside math delimiters $f(x)=\frac{ \hide{4-\sqrt{x}} }{e^x}$.\par
\vspace{\baselineskip}\hrule\vspace{\baselineskip}
\begin{luacode}
    for i,v in ipairs(list) do
        --texio.write_nl(v)
        tex.sprint ( '\fbox{'..v..'} \ ' )
    end
\end{luacode}
\end{document}

The second link also indicates that it is possible to process math styles differently, but due to the reasons explained here, it is not working very ideally.

As a matter of fact, it is possible to achieve your goals with LaTeX only. Try the code below.

\documentclass{article}
\usepackage{xcolor}
\usepackage{expl3}
\setlength\parindent{0pt}
\renewcommand{\baselinestretch}{1.5}
\everymath{\displaystyle}
% select version by using \finaltrue or \finalfalse
\newif\iffinal
%\finaltrue
\finalfalse
\ExplSyntaxOn
\seq_new:N \g_my_keys_seq
\cs_set:Npn \hide #1 {
    % check if in math mode
    \relax\ifmmode
        \seq_gput_right:Nn \g_my_keys_seq {$#1$}
    \else
        % normal text mode
        \seq_gput_right:Nn \g_my_keys_seq {#1}
    \fi
    % instead of making things white, we simply create a placeholder with the same dimensions
    % this prevents the learners from copying the answer from a PDF viewer
    \iffinal
        \phantom{#1}
    \else
        \textcolor{red}{#1}
    \fi
}
\tl_set:Nx \pivalue {\fp_use:N \c_pi_fp}
\ExplSyntaxOff
\begin{document}
Try with \hide{text}.\par
Try with \hide{LUA \pivalue}.\par
Try with \hide{\textbf{command}}.\par
Try with \hide{math mode $\pi$ inside}.\par
Try with inside math mode $\hide{\pi}$.\par
Try with inside math delimiters $f(x)=( \ \hide{5-x^2}\ ) e^x$.\par
Try with inside math delimiters $f(x)=\frac{ \hide{4-\sqrt{x}} }{e^x}$.\par
\vspace{\baselineskip}\hrule\vspace{\baselineskip}
\ExplSyntaxOn
% shuffle keys
\seq_shuffle:N \g_my_keys_seq
\seq_map_inline:Nn \g_my_keys_seq {
    \fbox{#1}\ 
}
\ExplSyntaxOff
\end{document}