For loop with keys of property list

Question

I am using a properties list and I would like to be able to create a command that produces the list of keys to be used to generate a for loop. I am currently using \prop_map_inline to generate all the keys but if I use this in the for loop it is interpreted as a single item and not a collection of several items.

This is an example code:

\documentclass{article}
\usepackage{ifthen}
\usepackage{xparse}
\ExplSyntaxOn
    \prop_new:N \g_persons_prop
% Create a new person
\NewDocumentCommand{\CreatePerson}{m} {
    \prop_gput:Nnn \g_persons_prop { #1 }
}

% Gets all persons
\NewDocumentCommand{\GetAllPersonKeys}{}{
    \prop_map_inline:Nn \g_persons_prop {
        ##1, 
    }
}

\ExplSyntaxOff
\CreatePerson{jd}{John Doe}
\CreatePerson{ad}{Albert Dull}
\CreatePerson{bu}{Ben Under}
\begin{document}
    I would like to have this:
    \makeatletter
        \begin{itemize}
            @for\sun:={jd, ad, bu}\do{\item We have person: \sun. }
        \end{itemize}
     \makeatother
But I get this instead:

\makeatletter
    \begin{itemize}
        \@for\sun:={\GetAllPersonKeys}\do{\item We have person: \sun. }
    \end{itemize}
 \makeatother   


\end{document}

What do you really want to do? Why not just prop_map_inline ... {We have person: ...}? — user202729, May 10 '22 at 15:01
If you want some keywords to learn yourself, there are 2 issues here • GetAllPersonKeys as implemented as not expandable, and • you didn't even try to expand it before executing @for, so no guarantee. — user202729, May 10 '22 at 15:03
I want to be able to use @for over the keys, in this case jd, ad, bu. I want this because I want to be able to do general loops in which I use the keys. I want to avoid having \ExplSyntaxOn on the main code (I am working on a class). The points you mention in your third comment are my issue. I do not know how to expand it such that it can be used. I tried googling but I could not find an answer I could extrapolate to this case. — gorkiana, May 10 '22 at 15:14
TeX programming is hard, if you don't learn it properly you'll get full of surprises. I guess if you want you can start at package writing - Where do I start LaTeX programming? - TeX - LaTeX Stack Exchange. — user202729, May 10 '22 at 15:30
Back to this point, it looks like that \@for f-expand the argument. So you have to use something f-expandable, such as \use:e's \expanded emulation plus some other prop_map function that is hollow-star. Try it yourself, if \tl_show:f {\GetAllPersonKeys} shows the correct comma-separated result you know it's correct. — user202729, May 10 '22 at 15:32
Alternatively if you allow some interface change, change the interface to \GetAllPersonKeys \@for \sun :={\AllPersonKeysResult} \do {...} it would be much easier to implement. — user202729, May 10 '22 at 15:33
Thank you for your comments. I do not understand you last comment. What are you proposing? Something like \edef\AllPersonKeysResult{\GetAllPersonKeys}? I tried it and it also does not work. Coul you explain it more? — gorkiana, May 10 '22 at 15:51
\GetAllPersonsKeys is not expandable so you can't use it there. You could define it so that it fills a suitable command, but on the whole you are only making your live difficult by missing expl3 with @for like this. Stick to one system. — Ulrike Fischer, May 10 '22 at 16:12
Thanks @UlrikeFischer! Then what would be the alternative without using expl3? I mean, how can I replace the property lists? — gorkiana, May 10 '22 at 16:23
Well expl3 is implemented using just TeX after all, so if you are good enough at TeX you can reimplement everything you want. I don't recommend it though — user202729, May 10 '22 at 16:44
I said that, there exists an implementation such that \GetAllPersonKeys \@for \sun :={\AllPersonKeysResult} \do {...} does what you want, but you need the initial \GetAllPersonKeys to be outside. If you're happy with that the answer would be simpler. — user202729, May 10 '22 at 16:49

score 1 · Accepted Answer · answered May 10 '22 at 16:36

You can map over the keys in expl3 too:

\documentclass{article}
\usepackage{ifthen}
\usepackage{xparse}
\ExplSyntaxOn
    \prop_new:N \g_persons_prop
% Create a new person
\NewDocumentCommand{\CreatePerson}{m} {
    \prop_gput:Nnn \g_persons_prop { #1 }
}

\NewDocumentCommand{\MapAllPersonKeys}{m}{
    \prop_map_inline:Nn \g_persons_prop {
       #1
    }
}



\ExplSyntaxOff
\CreatePerson{jd}{John Doe}
\CreatePerson{ad}{Albert Dull}
\CreatePerson{bu}{Ben Under}
\begin{document}
    I would like to have this:
  \makeatletter
    \begin{itemize}
        \@for\sun:={jd, ad, bu}\do{\item We have person: \sun. }
    \end{itemize}
 \makeatother

  \begin{itemize}
       \MapAllPersonKeys{\item we have person: #1!}
  \end{itemize}



\end{document}

Thanks a lot! This is quite magical. Do I understand correctly that it replaces #1 in the command definition by #1 when calling as you propose? — gorkiana, May 10 '22 at 17:03

For loop with keys of property list

1 Answers1