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I found a macro, counting the number of occurrences of a substring, as an answer to a different question. This does exactly what I want, at least, when just printing its output to the document. I want to use the output, and pass it on to a different command -- specifically, to the \bookmark[level=] value. I cannot figure out how to get it to expand, or how to capture its output. I am sure this is very trivial, and maybe I am simply missing the vocabulary to search for this -- but I would appreciate any help.

The code in question:

\ExplSyntaxOn
% \CountSubStr{<substring>}{<string>}
\NewDocumentCommand{\CountSubStr}{ m m }{
  \seq_set_split:Nnn \l_tmpa_seq { #1 } { #2 }
  \int_eval:n {(\seq_count:N \l_tmpa_seq) - 1 }
}
\ExplSyntaxOff
Jofkos
  • 111
  • Can you provide a complete example? What package is the \bookmark from? – mrCarnivore May 13 '23 at 19:10
  • tl;dr: "I am sure this is very trivial" → No, it's impossible. Unless you modify the thing to store the result somewhere (as in the answer below that stores it into a counter) that "is expandable" (\thesubstringcount). – user202729 May 14 '23 at 02:28

1 Answers1

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Not sure how you want \bookmark to work with \CountSubStr but this should work:

\documentclass{article}

\usepackage{bookmark}


\newcounter{substringcount}


\ExplSyntaxOn


% \CountSubStr{<substring>}{<string>}
\NewDocumentCommand{\CountSubStr}{ m m }
{
    \seq_set_split:Nnn \l_tmpa_seq { #1 } { #2 }
    \setcounter{substringcount}{ \int_eval:n {(\seq_count:N \l_tmpa_seq) - 1 } }
}
\ExplSyntaxOff


\bookmark[level=\thesubstringcount]{Last page}


\begin{document}
    Hello
    \CountSubStr{ab}{abcdeab}
\end{document}
mrCarnivore
  • 1,505
  • Using \NewExpandableDocumentCommand doesn't magically turn unexpandable functions into expandable. And \seq_set_split:Nnn is unexpandable, because it must do assignments. Neither \setcounter is expandable, by the way. – egreg May 13 '23 at 21:02
  • @egreg: It does not have to be since I assign the result to a counter and then use the counter when I need the result of the function… – mrCarnivore May 13 '23 at 21:11
  • I was mainly objecting to the usage of \NewExpandableDocumentCommand, which is wrong in that context. – egreg May 13 '23 at 21:23
  • as the content of your function is not expandable, you can simply use \NewDocumentCommand, it doesn't change anything. And why do you expect the bookmark to use the correct value if the bookmark is before the command?? – Ulrike Fischer May 13 '23 at 21:23
  • @egreg: It was from a previous attempt with a different solution. I did not think it did any harm leaving it in. Apparently I was wrong. I have now removed the wrong part. – mrCarnivore May 13 '23 at 21:25
  • @UlrikeFischer: I do not understand your point: \bookmark is placed AFTER the command. Maybe I do not understand the bookmark command but no example was provided... – mrCarnivore May 13 '23 at 21:27
  • it is place after the definition, but before the execution. At this point the counter is simply 0. – Ulrike Fischer May 13 '23 at 21:27
  • @UlrikeFischer: Ok. I guess me not noticing that also comes down to the missing MWE... Thanks for the hint. – mrCarnivore May 13 '23 at 21:41
  • So having an external counter is the only possibility here? There's no way to have that command expandable – or to somehow directly capture its output – because it uses an intermediate variable? Or maybe, different question, is there a way to count the occurrences of a substring, that is expandable? – Jofkos May 15 '23 at 05:29