General ⇒ expl3 for dummies

[erwann]

I would I rewrite this code inside a package (*.dtx) using expl3?

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\def\the@cartoon
	{
		Betty Boop
	}

[Stefan Kottwitz]

For example:

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\tl_const:Nn \c_the_cartoon {Betty\ Boop}

Test example:

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\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn

\tl_const:Nn \c_the_cartoon {Betty\ Boop}

\NewDocumentCommand { \thecartoon } { }
  {
    \tl_use:N \c_the_cartoon
  }
  

\ExplSyntaxOff
\begin{document}
\thecartoon
\end{document}

Stefan

[erwann]

Would it be possible to have an example showing how '\use:n' would come in handy? (page 16 of interface3.pdf)

[cgnieder]

I would I rewrite this code inside a package (*.dtx) using expl3?

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\def\the@cartoon
	{
		Betty Boop
	}

That depends. Is \the@cartoon going to be a tokenlist that is never going to change? Or may it be that its value (definition) changes (maybe depending on user settings)?

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% constant public variable:
\tl_const:Nn \c_mypackage_cartoon_tl {Betty~ Boop}

% constant internal variable:
\tl_const:Nn \c__mypackage_cartoon_tl {Betty~ Boop}

% public variable:
\tl_new:N \l_mypackage_cartoon_tl
\tl_set:N \l_mypackage_cartoon_tl {Betty~ Boop}

% internal variable:
\tl_new:N \l__mypackage_cartoon_tl
\tl_set:N \l__mypackage_cartoon_tl {Betty~ Boop}

I have written a fes packages with expl3 (have a look at the source codes of chemmacros, chemformula, leadsheets or xsim for example) and have barely ever used \use:n.

It is hard to give more than general advice on such a general question. It is much easier to give example on how to solve concrete problems.

[erwann]

Thank you for all the feedback. These guideline conforming macro names are long, is there not such a thing similar to namespaces?

[cgnieder]

No in TeX/LaTeX there is no namespace. This is part of the reason for the naming convention. The other reason is readability. After getting accustomed to the convention the code is far easier to read and understand than “traditional” (La)TeX code.

[erwann]

Two undescores for internal, one for public TL's. ExplSyntaxOn/Off inside 'document' environment seems odd, or I am missing something?

[cgnieder]

Two undescores for internal, one for public TL's.

Not only tokenlists but all kinds of variables, even functions. Public means that those variables and functions are allowed to be used by others and ideally are documented (just like all those in interface3). Internal functions and variables are not meant to be used by anyone (which also means there is no need to document them):

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\l_module_name_tl % local public tokenlist
\l__module_name_tl % local internal token list
\g_module_name_tl % global public tokenlist
\g__module_name_tl % global internal token list
\l_module_name_int % local public integer
\l__module_name_int % local internal integer
...
\module_name:n % public function with one brace group argument
\__module_name:n % internal function with one brace group argument

ExplSyntaxOn/Off inside 'document' environment seems odd, or I am missing something?

Quite true. I never do that in my real world documents. Only in the preamble or in packages.

[erwann]

Funny that the last response is attributed to someone other than myself.

Screen Shot 2018-03-15 at 7.37.08 PM.png (24.56 KiB) Viewed 12194 times

[erwann]

I would need, if possible, some clarification as to what the intended purposes of local public, local internal, global public, and public function are.

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\l_module_name_tl % local public tokenlist
    \l__module_name_tl % local internal token list
    \g_module_name_tl % global public tokenlist
    \g__module_name_tl % global internal token list
    \l_module_name_int % local public integer
    \l__module_name_int % local internal integer
    ...
    \module_name:n % public function with one brace group argument
    \__module_name:n % internal function with one brace group argument