Help integrating some Lua code into a Luatex document?

Question

Consider the following MWE:

\documentclass[12pt,a4paper]{amsart}
\usepackage{fontspec}
\usepackage{luacode}


\begin{document}
 ABC 

\begin{luacode}
  tex.sprint(os.date("compiled on --- %A at %X " ) )
\end{luacode}

\end{document}

As expected the output is ABC compiled on --- Saturday at 2:03:04 .

Now I would like to place this output in a footnote (or other inconspicuous place) in the document. So I tried using footnote{} like this.

\footnote{
\begin{luacode}
  tex.sprint(os.date("compiled on --- %A at %X " ) )
\end{luacode}
}

The resulting document doesn't compile in Luatex.

It is my understanding that the error (attached below) seems to be that somehow the % sign in lua is forcing latex to ignore the \end{luacode} . But the whole point of using package luacode was to avoid that problem.

How can I fix it?

Here is part of the error log:

I've run across a }' that doesn't seem to match anything.
For example,\def\a#1{...}' and \a}' would produce
this error. If you simply proceed now, the\par' that
I've just inserted will cause me to report a runaway
argument that might be the root of the problem. But if
your }' was spurious, just type2' and it will go away.


Runaway argument?
ex.sprint(os.date("compiled on \end {luacode} \@finalstrut \strutbox 
! Paragraph ended before \luacode@grab@lines was complete.
 
\par 
l.24 }

I suspect you've forgotten a `}', causing me to apply this
control sequence to too much text. How can we recover?
My plan is to forget the whole thing and hope for the best.

! Extra }, or forgotten \endgroup.
 }

l.24 }

I've deleted a group-closing symbol because it seems to be
spurious, as in $x}$'. But perhaps the } is legitimate and
you forgot something else, as in\hbox{$x}'. In such cases
the way to recover is to insert both the forgotten and the
deleted material, e.g., by typing `I$}'.

! Extra }, or forgotten \endgroup.
\H@@footnotetext ...t \strutbox }\color@endgroup }

l.24 }

I've deleted a group-closing symbol because it seems to be
spurious, as in $x}$'. But perhaps the } is legitimate and
you forgot something else, as in\hbox{$x}'. In such cases
the way to recover is to insert both the forgotten and the
deleted material, e.g., by typing `I$}'.

! LaTeX Error: \begin{luacode} on input line 24 ended by \end{document}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H   for immediate help.
 ...                                              

l.33 \end{document}

Answer 1

The luacode environment cannot be the argument to another command, similarly to verbatim environment. The reason is the usual one: category codes cannot be changed once the token list has been absorbed as an argument; the culprit here is obviously % that's a comment character when \footnote starts absorbing its argument.

It's recommended to have it in the preamble, in general, and to define Lua functions.

\documentclass[12pt,a4paper]{amsart}
\usepackage{fontspec}
\usepackage{luacode}

\begin{luacode}
  function compiledon()
    tex.sprint(os.date("compiled on --- %A at %X " ) )
  end
\end{luacode}
\newcommand{\compiledon}{\directlua{compiledon()}}

\setlength{\textheight}{2cm} % just for the example

\begin{document}

ABC\footnote{\compiledon}

\end{document}

You don't need to define \compiledon and simply use \directlua{compiledon()}, but this way it's cleaner, in my opinion.