luacode 适用于 \newcommand，但不适用于 \NewDocumentCommand

Question

想象一下以下代码：

\documentclass{book}

\usepackage{luacode}
\usepackage{xparse}

\NewDocumentCommand{\HelloWorld}{}{Hello World}
\newcommand{\DefaultHelloWorld}{Hello World}

\begin{luacode}
    luatexbase.add_to_callback("wrapup_run", function()
        io.write("\HelloWorld")
        -- io.write("\DefaultHelloWorld")
    end, "Post-process pdf")
\end{luacode}

\begin{document}
    Hello World!
\end{document}

为什么使用\newcommand可以正常工作并扩展为io.write("Hello World")，但一旦我切换到 ，\NewDocumentCommand就会出现以下错误（日志文件的摘录）：

Package: xparse 2023-10-10 L3 Experimental document command parser
)[\directlua]:2: invalid escape sequence near '"\H'.
\luacode@dbg@exec ...code@maybe@printdbg {#1} #1 }
                                           
l.14 \end{luacode}
           
The lua interpreter ran into a problem, so the
remainder of this lua chunk will be ignored.

Answer 1

谢谢乌尔丽克·菲舍尔

只需切换到\NewExpandableDocumentCommand：

\documentclass{book}

\usepackage{luacode}
% \usepackage{xparse} % REMOVED -- see @David Carlisle's comment

\NewDocumentCommand{\OldHelloWorld}{}{Hello World}        % OLD
\NewExpandableDocumentCommand{\HelloWorld}{}{Hello World} % NEW -- working
\newcommand{\DefaultHelloWorld}{Hello World}

\begin{luacode}
    luatexbase.add_to_callback("wrapup_run", function()
        io.write("\HelloWorld")
        -- io.write("\DefaultHelloWorld")
    end, "Post-process pdf")
\end{luacode}

\begin{document}
    Hello World!
\end{document}