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I have a token list that includes (at least) one non-expandable command (defined by \NewDocumentCommand) and want to write the result to a log file (lets assume the critical command generates character tokens only). Is there any way to enforce the execution to get the result (before shipout)?

Edit

@jlab asked for a MnWE. Well, since I don't know a solution I can only provide code that obviously does not work.

\documentclass{scrartcl} \NewDocumentCommand{\foo}{m}{#1xyz} % Well, the original is more complicated and not by me \begin{document} \newwrite\myfile \immediate\openout\myfile=bar.txt \immediate\write\myfile{\foo{abc}} % I get "\foo {abc}", but want "abcxyz" \end{document}
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  • in classical tex the answer is no , in luatex you could in principle typeset to a box then traverse the node list to get the font character nodes then iterate the node list, reversing any to unicode map and obtain a list of unicode characters as the result. Commented Jul 15 at 19:09
  • @DavidCarlisle: Thank you. lualatex would be fine, however, I have not much experience there. (I know Lua, but not the interfaces to LaTeX beside simple tex.sprint etc.), Commented Jul 15 at 19:10
  • as I indicated while it's possible it is rather fragile and not really in the tex spirit, I would say 99 times out of 100 such a question would have a different answer (eg arranging that the commands were not \protected so they simply expanded to characters). What is your actual use case here? Commented Jul 15 at 19:14
  • Sorry, I don't want to hurt the TeX spirit :-) My use case: I want to expand a package that generates data (and arranges them in a graphic) to get a logging of that very data. Unfortunately, the data (more precise: labeling) generation is done by a bunch of commands where a least the top level is non-expandable. Commented Jul 15 at 19:23
  • @Matthias Could you please provide a compilable test code that illustrate your particular issue? Commented Jul 15 at 19:35

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TeX commands don't really return anything. But in Luatex you can typeset into a box then inspect the box contents. Here I assume Unicode fonts so I can simply print characters, and print any white space as a normal space, and ignore everything else.

The command \foo is \protected and could not be defined as expandable.

It produces

xyz a A and B this that

for the two examples given,

\documentclass{article} \NewDocumentCommand\foo{O{X}}{a #1 and \char\numexpr`#1+1\relax} \NewDocumentCommand\writetolog{m}{% \setbox0\hbox{#1}% \directlua{ texio.write_nl("") for n in node.traverse(tex.box[0].head) do if n.id==12 then texio.write (" ") end if n.id==29 then texio.write(string.char(n.char)) end end texio.write_nl("") }} \begin{document} \writetolog{xyz \foo[A]} \writetolog{ this \textbf{that}} \end{document}
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  • Thank you, that was helpful. I wasn't aware that a \setbox already "calculates" its content, but thought, it is only "saved" for later. Commented Jul 15 at 20:12
  • @Matthias no if you want to "save for later" you use a macro so \def\foobar{xyz \foo[A]} or \newcommand or whatever instead of \def. Boxes really typeset their content and save a fragment of tex's almost final form just before it is converted to dvi or pdf by the back end Commented Jul 15 at 20:17

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