how to convert number to string in a variable name?

Question

I know that \fp_new_variable:n ⟨identifier⟩ must consist entirely of Latin letters from [a-zA-Z]. In the \setvar command below, I want to replace any numbers or underscores in the parameter #1 before using it, for example, convert h_2 to hUnderscoreTwo, and then let \fp_set_variable uses it. However, \fp_set_variable:nn doesn't seem to expand #1. Is there any way to achieve this?

\documentclass[12pt]{article}
\ExplSyntaxOn
\seq_new:N \g__xcn_var_list_seq
\NewDocumentCommand{\setvar}{mm}
{
 \seq_if_in:NnF \g__xcn_var_list_seq {#1 }
 {
 \fp_new_variable:n {#1}
 \seq_gput_left:Nn \g__xcn_var_list_seq {#1}
 } 
 \fp_set_variable:nn {#1} {#2} 
}
\NewExpandableDocumentCommand{\usevar}{O{15}m}
{ 
 \fp_eval:n { round( #2 , #1 ) }
}
\ExplSyntaxOff
\begin{document}
\setvar{h}{600 * 2}
\usevar{h}
%\setvar{h_2}{600 * 2} \usevar{h_2}
\end{document}

• David Carlisle: as always in expl3, given However, \fp_set_variable:nn doesn't seem to expand #1 you could use (or declare if necessary) an \fp_set_variable:en that does expand #1
• cfr: you can use l3regex to do the replacement in combination with the variant @DavidCarlisle mentioned. or use \exp_args:N....
• cfr: I don't think you should delete your question. but I think it would be better to start from one of the answers which does what you want and ask e.g. whether the syntax can be modified in whichever way you need. your question did not say why you didn't want to use the expandable answers, so it just seemed weird to be asking how to change my answer to do what the other answers already gave you.
• xcn: @cfr yes. You're right. Now I restore it if I could find it.
• xcn: @cfr yes, I have solved that.

Answer 1

You can do it by associating to the "external" name a "purified" internal one. But this will be much slower, mind you.

\documentclass[12pt]{article}
\ExplSyntaxOn
\prop_new:N \g__xcn_var_list_prop
\tl_new:N \l__xcn_var_purified_tl
\NewDocumentCommand{\setvar}{mm}
 {
 \__xcn_var_purify:n {#1}
 \prop_if_in:NnF \g__xcn_var_list_prop {#1 }
 {
 \exp_args:NV \fp_new_variable:n \l__xcn_var_purified_tl
 \prop_gput:NnV \g__xcn_var_list_prop {#1} \l__xcn_var_purified_tl
 }
 \exp_args:NV \fp_set_variable:nn \l__xcn_var_purified_tl {#2} 
 }
\NewExpandableDocumentCommand{\usevar}{O{15}m}
 { 
 \fp_eval:n { round( \prop_item:Nn \g__xcn_var_list_prop {#2} , #1 ) }
 }
\cs_new_protected:Nn \__xcn_var_purify:n
 {
 \tl_set:Nn \l__xcn_var_purified_tl {#1}
 \exp_args:NNe \tl_replace_all:Nnn \l__xcn_var_purified_tl
 { \char_generate:nn { `_ } {8} } % underscore
 { underscore }
 \regex_replace_all:nnN { ([0-9]+) } { \c{int_to_roman:n} {1円} } \l__xcn_var_purified_tl
 \tl_set:Ne \l__xcn_var_purified_tl { \l__xcn_var_purified_tl }
 }
\ExplSyntaxOff
\begin{document}
\setvar{h}{600 * 2}
\usevar{h}
\setvar{h_2}{600 * 2} \usevar{h_2}
\setvar{h_2}{2*pi} \usevar{h_2}
\fpeval{\usevar{h_2}/2}
\end{document}

output

• xcn: Can the syntax be modified so that I can use variable directly? such as use \setvar{h_c}{600 * 2 + h_b} instead if \setvar{h_c}{600 * 2 + \usevar{h_b} } .
• egreg: @xcn NO, it’s not possible, because variables cannot have names containing nonletters.
• xcn: it’s possible if change your answer a little.

Answer 2

In OpTeX, we can use \expr macro:

\mathinexpr
\def\_decdigits{15}
\def\setvar#1#2{\directlua{#1 = #2}}
\def\usevar#1{\nnum{\expr{#1}}}
\setvar{h}{600 * 2}
\usevar{h}
\setvar{h_2}{600 * 2} \usevar{h_2}
\setvar{h_2}{2*pi} \usevar{h_2}
\usevar{h_2/2}
\bye

The result is the same as in the egreg's answer.

• xcn: How to use Optex? I can't find Optex Compiler in Texworks editor.
• wipet: I don't know what Texworks editor is. If you are unable to find OpTeX in the editor menu then it is problem of this editor. TeXlive and MikTeX include OpTeX (you can use command line with optex command).

Answer 3

This modified answer allows to use understore in argument #2 of \setvar command.

\documentclass[12pt]{article}
\ExplSyntaxOn
\prop_new:N \g__xcn_var_list_prop
\tl_new:N \l__xcn_var_purified_tl
\tl_new:N \l__xcn_var_purifiedeq_tl
\NewDocumentCommand{\setvar}{mm}
 {
 \__xcn_var_purify:n {#1}
 \prop_if_in:NnF \g__xcn_var_list_prop {#1 }
 {
 \exp_args:NV \fp_new_variable:n \l__xcn_var_purified_tl
 \prop_gput:NnV \g__xcn_var_list_prop {#1} \l__xcn_var_purified_tl
 }
 \tl_set_eq:NN \l__xcn_var_purifiedeq_tl \l__xcn_var_purified_tl 
 \__xcn_var_purify:n {#2}
 \exp_args:NV \fp_set_variable:nn \l__xcn_var_purifiedeq_tl \l__xcn_var_purified_tl 
 }
\NewExpandableDocumentCommand{\usevar}{O{15}m}
 { 
 \fp_eval:n { round( \prop_item:Nn \g__xcn_var_list_prop {#2} , #1 ) }
 }
\cs_new_protected:Nn \__xcn_var_purify:n
 {
 \tl_set:Nn \l__xcn_var_purified_tl {#1}
 \exp_args:NNe \tl_replace_all:Nnn \l__xcn_var_purified_tl
 { \char_generate:nn { `_ } {8} } % underscore
 { U }
 %\regex_replace_all:nnN { ([0-9]+) } { \c{int_to_roman:n} {1円} } \l__xcn_var_purified_tl
 \tl_set:Ne \l__xcn_var_purified_tl { \l__xcn_var_purified_tl }
 }
\ExplSyntaxOff
\begin{document}
\setvar{h_a}{600 * 2}
\usevar{h_a}
\fpeval{\usevar{h_a}/2}
\setvar{h_b}{3.14+h_a}
\usevar{h_b}
\end{document}