LaTeX3 equivalent of C enumeration type

Question

I'm having to store a non-binary status, what would be the more idiomatic LaTeX3 way of doing it? For instance, suppose that there are 3 possible ways to format a manuscript: long/short/medium. What is the best way to do it in LaTeX3?

I can think of multiple possibilities:

1. Defining a bunch of int_const constants (fixed at 1, 2, 3, etc.) to name the possible states and then use a global integer int_new to store the current state.

   This seems straightforward, but also very expensive. If my understanding is correct, each integer constant takes a counter register in the current LaTeX3 design.

2. Using tokens to represent the possible states. In this case, I'd like the tokens used for the possible states to be declared before usage in the code for readability. So, one could have a tl_const (equal to 1, 2, 3, etc. for each possible state) and then use a global token list variable to hold the current state.

   This seems more efficient and possibly even more straightforward, but I do not like my "enum" labels to be named as c_xxx_xxx_tl since I think that naming them as token lists worsens the readability of the code.

Any idea on the matter?

Answer 1

Here is an example of the approach mentioned in the comments.

For each value <foo> of the enumeration, we define a new function \c_<foo>_manuscript which has \c_<foo>_manuscript_undefined: as its replacement text. (The real quark-like approach would be making it expand to \c_<foo>_manuscript itself, but in my experience expanding to an undefined control sequence works equally fine and is easier to debug in case of an unexpected expansion of the function.)

So the "enumeration" looks like

\cs_new_protected:Npn \c_short_manuscript  { \c_short_manuscript_undefined:  }
\cs_new_protected:Npn \c_medium_manuscript { \c_medium_manuscript_undefined: }
\cs_new_protected:Npn \c_long_manuscript   { \c_long_manuscript_undefined:   }

Storing one of these values works by \let-assigning a control sequence to the corresponding constant:

\cs_set_eq:NN \g__callegar_cur_manuscript \c_medium_manuscript

Finally, to check the current value against a certain constant, we use

\cs_if_eq:NNTF \g__callegar_cur_manuscript \c_medium_manuscript { true } { false }

Full example document:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn

% The "enumeration" values
\cs_new_protected:Npn \c_short_manuscript  { \c_short_manuscript_undefined:  }
\cs_new_protected:Npn \c_medium_manuscript { \c_medium_manuscript_undefined: }
\cs_new_protected:Npn \c_long_manuscript   { \c_long_manuscript_undefined:   }

% CS holding the current manuscript type value
\cs_set_eq:NN \g__callegar_cur_manuscript \c_medium_manuscript


% Set current manuscript type
\NewDocumentCommand \SetManuscriptType { m } {
    \cs_if_exist:cTF { c_#1_manuscript }
        { \cs_set_eq:Nc \g__callegar_cur_manuscript { c_#1_manuscript } }
        { \PackageError { callegar } { Manuscript~type~`#1'~not~defined } { } }
}

% Switch over the current manuscript type 
\NewDocumentCommand \SwitchManuscriptType { +m+m+m } {
    \cs_if_eq:NNTF \g__callegar_cur_manuscript \c_short_manuscript { #1 } {
        \cs_if_eq:NNTF \g__callegar_cur_manuscript \c_medium_manuscript { #2 } {
            \cs_if_eq:NNTF \g__callegar_cur_manuscript \c_long_manuscript { #3 }
                { \PackageError { callegar } { Unknown~manuscript~type~set } { } }
        }
    }
}

\ExplSyntaxOff

\begin{document}

Current manuscript type: \SwitchManuscriptType{short}{medium}{long}

\SetManuscriptType{short}
Current manuscript type: \SwitchManuscriptType{short}{medium}{long}

\SetManuscriptType{long}
Current manuscript type: \SwitchManuscriptType{short}{medium}{long}

%\SetManuscriptType{extralong}

\end{document}