expl3 sequence name replaced by \s__seq when written to the .aux file

Question

I'm trying to adapt this egreg's answer but I'm facing a very strange phenomenon.

As shown by the following MCE, the similar lines that are supposed to be written to the .aux file:

\int_gset:Nn \g_integer_int {#1}
\seq_put_right:Nn \g_integers_seq {#1}

result on the expected one for the 1st one but, in the 2nd one, \g_integers_seq is changed in \s__seq!

Here is the .aux file's content:

\relax 
\ExplSyntaxOn
\int_gset:Nn \g_integer_int {1}
\seq_put_right:Nn \s__seq {1}
\ExplSyntaxOff
\ExplSyntaxOn
\int_gset:Nn \g_integer_int {2}
\seq_put_right:Nn \s__seq {2}
\ExplSyntaxOff

Do you see what's going on?

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

\seq_new:N \g_integers_seq
\int_new:N \g_integer_int

\NewDocumentCommand{\NewInteger}{m}
{
  \iow_now:cx { @auxout }
   {
    \token_to_str:N \ExplSyntaxOn
    ^^J
    \int_gset:Nn \g_integer_int {#1}
    ^^J
    \seq_put_right:Nn \g_integers_seq {#1}
    ^^J
    \token_to_str:N \ExplSyntaxOff
  }
}

\ExplSyntaxOff
\begin{document}
\NewInteger{1}
\NewInteger{2}
\end{document}

Because \g_integers_seq is not a protected command. – egreg May 08 '19 at 21:33 — egreg, May 08 '19 at 21:33

score 2 · Answer 1 · answered May 08 '19 at 21:36

2

\g_integers_seq is not a protected command and doesn't survive x expansion.

You simply do \iow_now:cn:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

\seq_new:N \g_integers_seq
\int_new:N \g_integer_int

\NewDocumentCommand{\NewInteger}{m}
{
  \iow_now:cn { @auxout }
   {
    \ExplSyntaxOn
    ^^J
    \int_gset:Nn \g_integer_int {#1}
    ^^J
    \seq_put_right:Nn \g_integers_seq {#1}
    ^^J
    \ExplSyntaxOff
  }
}

\ExplSyntaxOff
\begin{document}
\NewInteger{1}
\NewInteger{2}
\end{document}

The .aux file will be

\relax 
\ExplSyntaxOn 
\int_gset:Nn \g_integer_int {1}
\seq_put_right:Nn \g_integers_seq {1}
\ExplSyntaxOff 
\ExplSyntaxOn 
\int_gset:Nn \g_integer_int {2}
\seq_put_right:Nn \g_integers_seq {2}
\ExplSyntaxOff

In the code you quote, \iow_now:cx is necessary for doing the computation through \int_eval:n.

If you need to do computations, you need to protect \g_integers_seq from expansion with \exp_not:N or \token_to_str:N.

answered May 08 '19 at 21:36

egreg

1,121,712

OK but why \g_integer_int does survive x expansion? And where \s__seq does come from? – Denis Bitouzé May 08 '19 at 21:45
1

@DenisBitouzé Because it's an unexpandable token defined with \countdef. – egreg May 08 '19 at 21:48
Do you mean any \g_..._intis an unexpandable token defined with \countdef? – Denis Bitouzé May 08 '19 at 21:50
1

@DenisBitouzé Yes. Currently the LaTeX2e \newcount macro is used, for compatibility with the allocation mechanism. – egreg May 08 '19 at 21:53
And where the name s__seq does come from? – Denis Bitouzé May 09 '19 at 05:45
1

@DenisBitouzé It's the internal implementation of sequence variables. – egreg May 09 '19 at 06:16

expl3 sequence name replaced by \s__seq when written to the .aux file

1 Answers1