[Tex/LaTex] latex3 complaining about Undefined control sequence. But it is defined!

expl3latex3

I've tried pairing this down, but each time I do that I'm either correcting my mistake or something. So here's a slightly unwieldy MWE.

In a nutshell, what I'm trying to do is….

I'm writing a quiz that has multiple version. I've got some clunky LaTeX code that already handles versioning, but I decided I could probably get cleaner looking document code if I tried writing something using LaTeX3.

Each quiz has a version attached to it. I'm writing a \choice macro that's given a ; separated list of possible output which will change based upon the version of the quiz.

For example if I write \choice{x;y;z;w} then on version A of the quiz \choice will provide x, on version B of the quiz \choice will provide y, etc.

I'm not anywhere near getting this up and running. I'm actually not interested in someone telling me how to achieve my ultimate goal: I think I'll learn a fair amount if I try it on my own. Also, I know I'm not following notational conventions quite correctly, but it's giving me a headache trying to balance notation (which I still find difficult to read) and mastering syntax (which I find slightly obscure, but beginning to get the hang of).

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
%-@-(1)---------------------------------------------------------------------
%% --- VERSIONING --- %%
%% store what the possible version are
\tl_new:N  \g__version_types
\tl_set:Nn \g__version_types { a;b;c;d }
\tl_show:N \g__version_types
%% make a sequence of the possible versions
\seq_new:N \g__all_possible_versions_seq
\seq_gset_split:Nnn \g__all_possible_versions_seq { ; } {\g__version_types}
\seq_show:N \g__all_possible_versions_seq
%% allow the user to define what the versions are
\NewDocumentCommand{\defineversions}{ O{;} m }{
    \tl_set:Nn \g__version_types { #2 }
    \seq_set_split:Nnn \g__all_possible_versions_seq { #1 } \g__version_types
}
%-@-(2)---------------------------------------------------------------------
%% --- GETTING/SETTING VERSIONS ---%%
\tl_new:N   \g__tl_current_doc_version 

\cs_new:Npn \mv_set_version:n #1 
    {
        \tl_set:Nn \g__tl_current_doc_version { #1 }
    }

\cs_new:Npn \mv_get_version 
    {
        \tl_use:N \g__tl_current_doc_version
    }

\newcommand{\setversion}[1]{\mv_set_version:n {#1}}
\newcommand{\getversion}{ \mv_get_version }

\cs_new:Npn \mv_test_version:n #1 {
    \str_if_eq:VnTF \g__tl_current_doc_version { #1 } { HELLO } { BYE}
}
\newcommand{\testversion}[1]{\mv_test_version:n {#1}}

%-@-(3)---------------------------------------------------------------------
%% --- CREATING THE USER INTERFACE --- %%
%% I'm going to destructive examine the sequence, so make 
%% a copy of it and work with copy
\seq_new:N     \g__copy_all_possible_versions_seq
\seq_set_eq:NN \g__copy_all_possible_versions_seq \g__all_possible_versions_seq
\tl_new:N      \g__current_possible_version_tl
%% Information that the user passes to us
\seq_new:N \g__user_defined_choice_seq
\tl_new:N  \g__current_possible_choice_tl

%% This "cs" assumes that the user choices have been translated
%% into a sequence
\cs_new:Npn \__test_current_choice_against_version:n #1 { 
    \seq_pop_left:NN \g__user_defined_choice_seq        
                     \g__current_possible_choice_tl

    \seq_pop_left:NN \g__copy_all_possible_versions_seq 
                     \g__current_possible_version_tl

    \tl_use:N        \g__current_possible_choice_tl --
    \tl_use:N        \g__current_possible_version_tl \par

    \str_if_eq:VVTF  \g__current_possible_choice_tl 
                     \g__current_possible_version_tl
                     { \tl_use:N \g__current_possible_choice_tl  }
                     { #1 }
}

\cs_new:Npn \mv_make_choice:n #1 {
    \__test_current_choice_against_version:n
        { \__test_current_choice_against_version:n 
            { \__test_current_choice_against_version:n 
                { FAIL }}}
}

\NewDocumentCommand{\choices}{ O{;} m }{
    \texttt{#2}\par
    \seq_gset_split:Nnn \g__user_defined_choice_seq  {#1}  {#2}
    \mv_make_choice:n {#1}
}

\ExplSyntaxOff
\begin{document}

Hello:  I'm setting the version \setversion{b}

I'm getting the version \textbf{\getversion}!

Choosing \choices{x;y;z;w}
\end{document}

I'm getting an error about an empty sequence. I've tried showing the sequence, and tokens used to create it, but nothing seems to be right.

Best Answer

I've tried to correct it, but I don't know if it does exactly what you want:

\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
%-@-(1)---------------------------------------------------------------------
%% --- VERSIONING --- %%
%% store what the possible version are
\tl_new:N  \g__version_types_tl
\tl_set:Nn \g__version_types_tl { a;b;c;d }
%% make a sequence of the possible versions
\seq_new:N \g__all_possible_versions_seq
\seq_new:N \g__copy_all_possible_versions_seq
\cs_generate_variant:Nn \seq_gset_split:Nnn { NnV }
\seq_gset_split:NnV \g__all_possible_versions_seq { ; } \g__version_types_tl
\seq_gset_eq:NN \g__copy_all_possible_versions_seq \g__all_possible_versions_seq
%% allow the user to define what the versions are
\NewDocumentCommand{\defineversions}{ O{;} m }
 {
  \tl_gset:Nn \g__version_types_tl { #2 }
  \seq_gset_split:NnV \g__all_possible_versions_seq { #1 } \g__version_types_tl
  \seq_gset_eq:NN \g__copy_all_possible_versions_seq \g__all_possible_versions_seq
 }

%-@-(2)---------------------------------------------------------------------
%% --- GETTING/SETTING VERSIONS ---%%

\tl_new:N   \g__current_doc_version_tl

\cs_new_protected:Npn \mv_set_version:n #1 
 {
  \tl_set:Nn \g__current_doc_version_tl { #1 }
 }

\cs_new:Npn \mv_get_version:
 {
  \tl_use:N \g__current_doc_version_tl
 }

\NewDocumentCommand{\setversion}{m}
 {
  \mv_set_version:n {#1}
 }
\NewDocumentCommand{\getversion} {}
 {
  \mv_get_version:
 }

\cs_new:Npn \mv_test_version:n #1
 {
  \tl_if_eq:VnTF \g__tl_current_doc_version { #1 } { HELLO } { BYE}
 }
\NewDocumentCommand{\testversion}{m}
 {
  \mv_test_version:n {#1}
 }

%-@-(3)---------------------------------------------------------------------
%% --- CREATING THE USER INTERFACE --- %%
%% I'm going to destructively examine the sequence, so make 
%% a copy of it and work with copy
\tl_new:N  \g__current_possible_version_tl
%% Information that the user passes to us
\seq_new:N \g__user_defined_choice_seq
\tl_new:N  \g__current_possible_choice_tl

%% This "cs" assumes that the user choices have been translated
%% into a sequence
\cs_new_protected:Npn \__test_current_choice_against_version: 
 {
  %I'm working 
  \seq_gpop_left:NN \g__user_defined_choice_seq        
                    \g__current_possible_choice_tl

  \seq_gpop_left:NN \g__copy_all_possible_versions_seq 
                    \g__current_possible_version_tl

  \tl_if_eq:NNTF    \g__current_possible_choice_tl 
                    \g__current_possible_version_tl
                    { \tl_use:N \g__current_possible_choice_tl  }
                    { FAIL }
 }

\cs_new:Npn \mv_make_choice:n #1
 {
  \__test_current_choice_against_version:
 }

\NewDocumentCommand{\choices}{ O{;} m }
 {
  \texttt{#2}\par
  \seq_gset_split:Nnn \g__user_defined_choice_seq  {#1}  {#2}
  \mv_make_choice:n {#1}
 }

\ExplSyntaxOff
\begin{document}

Hello:  I'm setting the version \setversion{b}

I'm getting the version \textbf{\getversion}!

Choosing \choices{x;y;z;w}
\end{document}

I fixed the names and some programming glitches. For instance you're comparing token lists with \str_if_eq:... but \tl_if_eq:... should be used. In particular \tl_if_eq:NNTF and not \str_if_eq:VVTF which does more work for nothing. It's quite obscure why you define \mv_make_choice:n with an argument that you don't use. Just use \__test_current_choice_against_version: as the final instruction in \choices.

Other points.

When a variable is declared global, use only global assignments to it.
Don't forget that all functions should have a colon in their name.
Use \cs_new_protected:Npn when the function does unexpandable jobs (such as setting token lists or sequences).

Related Solutions

[Tex/LaTex] MacTeX 2019 gives “! LaTeX3 Error: Control sequence \not= already defined.”

The example fails also on my TeX Live (MacTeX) 2017, probably because of updates you didn't apply.

The problem is simple: you are using too many math font packages. Loading newtxmath before ebgaramond-maths is recommended, because the latter only acts on the operators and letters math groups, not on symbols and largesymbols.

If you load unicode-math, all these settings to math fonts will be completely discarded and you'd get Latin Modern Math.

If you add

\[
abc+\int f(x)\,dx
\]

to your test document and compile skipping past the errors, you get

Removing \usepackage{unicode-math} not only removes the errors, but produces

LaTeX3 not enforcing argument types for user-defined control sequences, why

The programming layer expl3 is still based on the TeX language and the lookup for arguments is as defined by TeX's rules.

These rules only distinguish between delimited and undelimited arguments. And what expl3 calls “functions” are actually regular TeX macros; variables, depending on their type, can be either macros or registers.

The basic \cs_new:Nn function for defining other functions only deals with undelimited arguments. It takes two arguments: one a single token, which should be a valid name for a function including the signature; the second argument should be a braced list of tokens.

The signature is used in order to supply the correct parameter text for the underlying macro to be defined, because a declaration such as

\cs_new:Nn \mymodule_foo:nn { #1 -- #2 }

eventually becomes

\def\mymodule_foo:nn #1#2{#1--#2}

(just like \newcommand does). It is possible to define functions without a signature in their name, but it's generally not recommended: these would be user level commands and it's better to use \NewDocumentCommand for them.

On the other hand, if you do

\cs_new:Nn \mymodule_foo:N { --#1-- }

and then call

\mymodule_foo:N {text}

TeX will follow its own rules and accept the code without complaining, notwithstanding that the coding is wrong from the expl3 point of view.

Why is it not enforced that arguments are specified in the proper way as regards to braced or nonbraced? Because this would be generally impossible and, in any case, it would introduce a heavy overhead in terms of speed and efficiency.

Best Answer

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[Tex/LaTex] MacTeX 2019 gives “! LaTeX3 Error: Control sequence \not= already defined.”

LaTeX3 not enforcing argument types for user-defined control sequences, why

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