2

MWE as follows:

\documentclass{article}

\begin{document}
\NewMirroredHookPair{cmd,test,begin}{cmd,test,end}
\def\testcmd{%
  \UseHook{cmd,test,begin}
  \def\TTTa{TTTa-val} % only '\gdef' can use '\\\TTTa'
  % \TTTa  % ---> works well.
  \\ \TTTa % ---> error: ! Undefined control sequence. <recently read> \TTTa 
  \UseHook{cmd,test,end}
}
\AddToHook{cmd,test,begin}{\fbox{BEGIN}\begin{tabular}{c}}
\AddToHook{cmd,test,end}{\end{tabular}\fbox{END}}
TEST: \testcmd
\end{document}

The above code can not compile, the error log is:

This is pdfTeX, Version 3.141592653-2.6-1.40.27 (TeX Live 2026/dev/Arch Linux) (preloaded format=pdflatex)
 restricted \write18 enabled.
entering extended mode
(./test.tex
LaTeX2e <2024-11-01> patch level 2
L3 programming layer <2025-01-18>
(/usr/share/texmf-dist/tex/latex/base/article.cls
Document Class: article 2024/06/29 v1.4n Standard LaTeX document class
(/usr/share/texmf-dist/tex/latex/base/size10.clo))
(/usr/share/texmf-dist/tex/latex/l3backend/l3backend-pdftex.def) (./test.aux)
! Undefined control sequence.
<recently read> \TTTa 
                      
l.52 TEST: \testcmd
                   
?

But if i:

  • use \TTTa inside \testcmd, it compiles.
  • remove these 2 \AddToHook about tabular, then both \TTTa and \\\TTTa can be used.
  • replace \def\TTTa by \gdef\TTTa, then both \TTTa and \\\TTTa can be used.

I'd like to use \\\TTTa together with \def\TTTa and these two tabular hooks. How can I achieve this ? Is it possible ?

Improve this question
2
  • why do you want a tabular with an empty first row? Commented Sep 15 at 15:32
  • @DavidCarlisle I am using longtable to replicate a comlex contentsline style from etoc package. The part before '\\' corresponds to the contents line title, which use \multicolumn. Commented Sep 15 at 15:40

1 Answer 1

Reset to default
5

this is not really related to hooks.

Every alignment cell is a group, so if you want the definition to be visible in all cells (and made with a non global definition) ensure the definition is before the alignment starts.

\documentclass{article}

\begin{document}
\NewMirroredHookPair{cmd,test,begin}{cmd,test,end}
\def\testcmd{{% extra group
  \def\TTTa{TTTa-val}% only '\gdef' can use '\\\TTTa' don't have space before %
  \UseHook{cmd,test,begin}% dont forget %
  % \TTTa  % ---> works well.
  \\ \TTTa % ---> error: ! Undefined control sequence. <recently read> \TTTa 
  \UseHook{cmd,test,end}% dont forget %
}}
\AddToHook{cmd,test,begin}{\fbox{BEGIN}\begin{tabular}{c}}
\AddToHook{cmd,test,end}{\end{tabular}\fbox{END}}
TEST: \testcmd
\end{document}
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