How to pass the the content from Lua function to a LaTeX3 token list (tl)?

Question

I have a Lua function that generates LaTeX content (a string containing LaTeX commands like "\\textbf{foo}") and it can be successfully outputted with \lua_now:n and tex.print(). Now I'm planning to record the content for the purpose of l3build regression test and I try to pass the content to a token list and then write it the log file with \tl_show:N. However the following code raises an error: Illegal parameter number in definition of \l__csl_bibliography_tl. Is there another approach?

\documentclass{article}
\usepackage{luacode}
\begin{luacode*}
function make_bibliography()
  local result = "\\textbf{Foo}"
  tex.print(result)
end
\end{luacode*}
\ExplSyntaxOn
\tl_new:N \l__csl_bibliography_tl
\cs_new:Npn \printbibliography
  {
    % \lua_now:n { make_bibliography() }   % It works fine.
    \tl_set:Nx \l__csl_bibliography_tl { \lua_now:n { make_bibliography() } }
    \tl_show:N \l__csl_bibliography_tl
    \tl_use:N \l__csl_bibliography_tl
  }
\ExplSyntaxOff
\begin{document}
\printbibliography
\end{document}

David Carlisle · Accepted Answer · 2022-09-23T08:35:04.297

9

You can set the tl (macro) from Lua:

\documentclass{article}
\usepackage{luacode}
\begin{luacode*}
function make_bibliography()
  local result = "\\textbf{Foo}"
  token.set_macro("l__csl_bibliography_tl",result)
end
\end{luacode*}
\ExplSyntaxOn
\tl_new:N \l__csl_bibliography_tl
\cs_new:Npn \printbibliography
  {
    \lua_now:n{ make_bibliography() }
    \tl_show:N \l__csl_bibliography_tl
    \tl_use:N \l__csl_bibliography_tl
  }
\ExplSyntaxOff
\begin{document}
\printbibliography
\end{document}

Note that token.set_macro does not handle the case where result contains e.g. a ~ character and the catcode of ~ is currently active.

Also any control sequences used (eg \textbf here) must already be in the hash table. See tilde ~ in lua adds a new line for some discussion of this.

edited Sep 23 '22 at 08:35

answered Sep 22 '22 at 14:34

David Carlisle

757,742

1

Note that token.set_macro does not handle the case where result contains e.g. a ~ character and the catcode of ~ is currently active correctly, as well as the case where some control sequence is in the string but not in the hash table. → luatex - tilde ~ in lua adds a new line - TeX - LaTeX Stack Exchange & linked questions from there. – user202729 Sep 23 '22 at 07:05
@user202729 yes, I stole your comment and added to my answer, thanks – David Carlisle Sep 23 '22 at 08:35

score 5 · Answer 2 · answered Sep 22 '22 at 14:41

The problem is that \textbf doesn't survive x-expansion. You can wrap the problematic construction with \text_expand:n:

\documentclass{article}
\usepackage{luacode}
\begin{luacode}
function make_bibliography()
  local result = "\textbf{Foo}"
  tex.print(result)
end
\end{luacode}
\ExplSyntaxOn
\tl_new:N \l__csl_bibliography_tl
\cs_new:Npn \printbibliography
  {
    \tl_set:Nx \l__csl_bibliography_tl { \text_expand:n { \lua_now:n { make_bibliography() } } }
    \tl_show:N \l__csl_bibliography_tl
    \tl_use:N \l__csl_bibliography_tl
  }
\ExplSyntaxOff
\begin{document}
\printbibliography
\end{document}

In the console you'll see

> \l__csl_bibliography_tl=\textbf {Foo}.

and the output is

I think Carlisle's approach is simpler because it involves less expansion control. Thank you all the same. — Zeping Lee, Sep 22 '22 at 16:00
@ZepingLee But it assumes that token lists variables are implemented as macros (which is true up to some point). — egreg, Sep 22 '22 at 16:07

How to pass the the content from Lua function to a LaTeX3 token list (tl)?

2 Answers2