LaTeX 3 string variable with braces

Question

I want to include some braces in my string variable:

\documentclass{article}
\usepackage{expl3}

\begin{document}
    \ExplSyntaxOn
    \str_new:N \l_example_var
    \int_new:N \l_example_int

    \str_set:Nn \l_example_var {\{}
    \str_put_right:NV \l_example_var {\l_example_int}
    \str_put_right:Nn \l_example_var {\}~some~text}

    \str_show:N \l_example_var
    \ExplSyntaxOff
\end{document}

Unfortunately this results in the braces being preceded by pesky backslashes:

> \l_example_var=\{0\} some text.
<recently read> }

l.13 ^^I\str_show:N \l_example_var

How would I be able to get rid of the backslashes in front of the braces? E.g. \l_example_var={0} some text.

Answer 1

I'm not sure what's the benefit of a string such as {42} and probably you need a token list instead. However,

\str_set:Nx \l_example_str { \c_left_brace_str \int_use:N \l_example_int \c_right_brace_str }

will do. For a token list it's similar

\tl_set:Nx \l_example_tl { { \int_use:N \l_example_int } }

Answer 2

Apparently, the { and } 'strings' shall appear literally in the string, so one way to add them is to use \c_left_brace_str and \c_right_brace_str and the V modifier for the \str_set:Nn macro

There are other literal string constants such as \c_hash_str or \c_dollar_str, which are constant token lists with catcode 12 actually. See page 75 in the current interface3 manual (as of 2018/12/27).

\documentclass{article}
\usepackage{expl3}

\begin{document}
    \ExplSyntaxOn
    \str_new:N \l_example_var
    \int_new:N \l_example_int

    \str_set:NV \l_example_var \c_left_brace_str
    \str_put_right:NV \l_example_var \l_example_int
    \str_put_right:NV \l_example_var \c_right_brace_str
    \str_put_right:Nn \l_example_var {~some~text}


    \str_show:N \l_example_var
    \ExplSyntaxOff
\end{document}

The output is

This is pdfTeX, Version 3.14159265-2.6-1.40.19 (TeX Live 2018)

(preloaded format=pdflatex) \write18 enabled. entering extended mode

(./stringwith.tex LaTeX2e <2018-12-01>

(/usr/local/texlive/2018/texmf-dist/tex/latex/base/article.cls

Document Class: article 2018/09/03 v1.4i Standard LaTeX document class

(/usr/local/texlive/2018/texmf-dist/tex/latex/base/size10.clo))

(/usr/local/texlive/2018/texmf-dist/tex/latex/l3kernel/expl3.sty

(/usr/local/texlive/2018/texmf-dist/tex/latex/l3kernel/expl3-code.tex)

(/usr/local/texlive/2018/texmf-dist/tex/latex/l3kernel/l3pdfmode.def))

(./stringwith.aux)

\l_example_var={0} some text. }

l.16 \str_show:N \l_example_var

? x No pages of output. Transcript written on stringwith.log.