Problem printing LaTeX from lua in lualatex

Question

I am having difficulty printing LaTeX from a lua function in a LaTeX document processed with lualatex (version 0.70.2). I have a sample that works (if I remove all newlines from the code) and a case that fails. I don't know why these get different results. Here is the sample that fails:

\documentclass{report}
\usepackage{luacode}
\begin{document}

\begin{luacode*}
tex.sprint([[
\begin{tabular}{ | l | l | p{4.in} | } 
\hline 
{\bf File} & {\bf Cards} & {\bf Summary} \\
\hline 
\end{tabular} ]])
\end{luacode*} 

\end{document}

I get an error saying:

! Misplaced \noalign.
\hline ->\noalign
              {\ifnum 0=`}\fi \hrule \@height \arrayrulewidth \futurelet...
l.22 \end{luacode*}

When I put all of the LaTeX code printed from lua on one line the code works fine:

\documentclass{report}
\usepackage{luacode}
\begin{document}

\begin{luacode*}
tex.sprint([[ \begin{tabular}{ | l | l | p{4.in} | } \hline {\bf File} &{\bf Cards} & {\bf Summary} \\ \hline \end{tabular} ]])
\end{luacode*} 

\end{document}

So I have a few question. First, why does the first example shown above fail? It seems like something I am not aware of is being inserted into the generated LaTeX.

Also is there a way for me to see the actual LaTeX that is generated and processed so that I can debug issues like this better? Is there a way to tell the lualatex to log the actual LaTeX it tries to process?

Any other suggestions for how to debug a problem like this?

Answer 1

The problem are the line ends:

tex.sprint([[
\begin{tabular}{ | l | l | p{4.in} | } 
\hline 
{\bf File} & {\bf Cards} & {\bf Summary} \\
\hline 
\end{tabular} ]])

The string encoded via [[ and ]] will contain characters with code 10 ("\n", new line character). When TeX gets the string from Lua, it takes it as whole line, thus the line ends does not get the usual treatment (replacing it including previous spaces, setting the character configured by \endlinechar). Instead the new line character is a normal character, the slot position in cmr10 is Ω.

Because there is a character, the Ω before \hline, the cell has already started and \hline complains, because it must be used at the begin of the row.

Possible workarounds:

• Without new lines as single strings:

  \begin{luacode*}
  tex.sprint(
  [[\begin{tabular}{ | l | l | p{3in} | }]],
  [[\hline]],
  [[\bfseries File & \bfseries Cards & \bfseries Summary \\]],
  [[\hline]],
  [[\end{tabular}]])
  \end{luacode*}
  

• Removing the new line char at TeX level with a category code for ignoring (9):

  \begingroup
  \catcode10=9\relax
  \begin{luacode*}
  tex.sprint([[
  \begin{tabular}{ | l | l | p{3in} | }
  \hline
  \bfseries File & \bfseries Cards & \bfseries Summary \\
  \hline
  \end{tabular}]])
  \end{luacode*} 
  \endgroup
  

  Also catcode tables can be used, if the catcode setting for slot 10 is 9.

• Split string in lines in Lua, see also question "Split string in lua?".

  \begin{luacode*}
  for line in unicode.utf8.gmatch([[
  \begin{tabular}{ | l | l | p{3in} | }
  \hline
  \bfseries File & \bfseries Cards & \bfseries Summary \\
  \hline
  \end{tabular}]],
  "[^\r\n]+") do tex.sprint(line) end
  \end{luacode*}
  

Full example:

\documentclass{report}
\usepackage{luacode}
\begin{document}

\begin{luacode*}
tex.sprint(
[[\begin{tabular}{ | l | l | p{3in} | }]],
[[\hline]],
[[\bfseries File & \bfseries Cards & \bfseries Summary \\]],
[[\hline]],
[[\end{tabular}]])
\end{luacode*}

\begingroup
\catcode10=9\relax
\begin{luacode*}
tex.sprint([[
\begin{tabular}{ | l | l | p{3in} | }
\hline
\bfseries File & \bfseries Cards & \bfseries Summary \\
\hline
\end{tabular}]])
\end{luacode*}
\endgroup

\begin{luacode*}
for line in unicode.utf8.gmatch([[
\begin{tabular}{ | l | l | p{3in} | }
\hline
\bfseries File & \bfseries Cards & \bfseries Summary \\
\hline
\end{tabular}]],
"[^\r\n]+") do tex.sprint(line) end
\end{luacode*}

\end{document}

Answer 2

You are using the wrong print command in the first example. Since you are entering multiple lines, these lines are not string any more. So, you can't use sprint in that case. You should've used texio.write_nl instead.

\documentclass{report}
\usepackage{luacode}
\begin{document}

\begin{luacode*}
texio.write_nl([[
\begin{tabular}{| l | l | p{4.in} | } 
\hline
{\bf File} & {\bf Cards} & {\bf Summary} \\  
\hline 
\end{tabular}]])
\end{luacode*} 

\end{document}

Then you get this as output:

Answer 3

use the environment luacode without the star and escape the backslashes:

\documentclass{report}
\usepackage{luacode}
\begin{document}

\begin{luacode}
tex.print("\\begin{tabular}{| l | l | p{4.in} | } \\hline")
tex.print("\\bfseries File & \\bfseries Cards & \\bfseries Summary \\\\\\hline") 
tex.print("\\end{tabular}")
\end{luacode} 

\end{document}