To help me learn l3keys I created two small demos.
The first uses l3keys for a command and seems to work correctly as far as I can tell.
% !TEX program = lualatexmk% !TEX encoding = UTF-8 Unicode\documentclass{article}\ExplSyntaxOn\prop_gput:Nnn \g_msg_module_type_prop { foo }{ Command }\msg_new:nnnn { foo }{ unknownoption } { Unknown~option. }{ Try~again~but~with~a~known~option. }\tl_new:N \l__foo_thing_tl\tl_new:N \l__foo_towhom_tl\keys_define:nn { foo } { thing .tl_set:N = \l__foo_thing_tl , thing .default:n = door , thing .initial:n = ice , towhom .tl_set:N = \l__foo_towhom_tl , towhom .default:n = Dana , towhom .initial:n = Ina , unknown .code:n = \msg_fatal:nn { foo }{ unknownoption } }\cs_new_protected:Npn \__foo_foo:nn #1#2 { \group_begin: \keys_set:nn { foo } { #1 } #2~\l__foo_thing_tl \c_space_tl to~\l__foo_towhom_tl. \group_end: }\DeclareDocumentCommand{ \foosetup } { m } { \keys_set:nn { foo } { #1 } }\DeclareDocumentCommand{ \foo } { O{} m } { \__foo_foo:nn { #1 } { #2 } }\ExplSyntaxOff\begin{document}This demo shows how to use \texttt{l3keys} for a command.\foo{Give the} \par\foo[thing]{Give the} \par\foo[thing,towhom]{Give the} \par\foo[thing=car,towhom=Tom]{Give the} \par\foosetup{thing=apple}\foo{Give the} \par\foo[towhom]{Give the} \par\end{document}Here is the output:
The second uses l3keys for a package and seems to work correctly except in one case where a key doesn't correctly initialize.
% !TEX program = lualatexmk% !TEX encoding = UTF-8 Unicode\begin{filecontents}[overwrite,noheader]{foopkg.sty}\ProvidesExplPackage{foopkg}{}{}{}\msg_new:nnnn { foopkg }{ unknownoption } { Unknown~option. }{ Try~again~but~with~a~known~option. }\tl_new:N \l__foopkg_thing_tl\tl_new:N \l__foopkg_towhom_tl\keys_define:nn { foopkg } { thing .tl_set:N = \l__foopkg_thing_tl , thing .default:n = door , thing .initial:n = ice , towhom .tl_set:N = \l__foopkg_towhom_tl , towhom .default:n = Dana , towhom .initial:n = Ina , unknown .code:n = \msg_fatal:nn { foopkg }{ unknownoption } }\ProcessKeyOptions[foopkg]\DeclareDocumentCommand{ \foosetup } { m } { \keys_set:nn { foopkg } { #1 } }\cs_new_protected:Npn \__foopkg_foo:nn #1#2 { \group_begin: \keys_set:nn { foopkg } { #1 } #2~\l__foopkg_thing_tl \c_space_tl to~\l__foopkg_towhom_tl. \group_end: }\DeclareDocumentCommand{ \foo } { O{} m } { \__foopkg_foo:nn { #1 } { #2 } }\end{filecontents}\documentclass{article}%\usepackage[thing=vase,towhom=Val]{foopkg}\usepackage{foopkg}\begin{document}This demo shows how to use \texttt{l3keys} for a package.\foo{Give the} \par\foosetup{thing=door}\foo{Give the} \par\foosetup{thing,towhom}\foo{Give the} \par\foosetup{thing=car,towhom=Tom}\foo{Give the} \par\foosetup{thing=apple}\foo{Give the} \par\foosetup{towhom}\foo{Give the} \par\end{document}Here is the output:
In the second demo, the second occurrence of Tom should ideally be Ina but I don't understand why the key doesn't reset. This question seems relevant but I'm already, I think, using the solution there and either I'm doing something wrong or I'm not understanding something simple. Can the two demos be made to give the same results?