我有许多与此结构相同的命令，我想知道是否可以压缩代码以避免必须输入两次E_{K和K_{\symup{trans}。我看不出有什么方法可以做到这一点而不产生破坏分组的问题。
我的 MWE：
% !TEX TS-program = lualatexmk
% !TEX encoding = UTF-8 Unicode
\documentclass{article}
% xparse is now automatically loaded
\NewDocumentCommand{\translationalkineticenergy}{ s d[] }{%
% d[] must be used because of the way consecutive optional
% arguments are handled. See xparse docs for details.
\IfBooleanTF{#1}%
{% We have a *.
\IfValueTF{#2}%
{%
E_{K{\symup{,}#2}}%
}%
{%
E_{K}%
}%
}%
{% We don't have a *.
\IfValueTF{#2}%
{%
K_{\symup{trans}{\textnormal{,}#2}}%
}%
{%
K_{\symup{trans}}%
}%
}%
}%
\begin{document}
\( \translationalkineticenergy \quad \translationalkineticenergy[\symup{final}]
\quad \translationalkineticenergy* \quad \translationalkineticenergy*[\symup{final}] \)
\end{document}
更新：在我等待的时候，我得到了这个新的 MWE。
% !TEX TS-program = lualatexmk
% !TEX encoding = UTF-8 Unicode
\documentclass{article}
% xparse is now automatically loaded
\NewDocumentCommand{\translationalkineticenergy}{ s d[] }{%
% d[] must be used because of the way consecutive optional
% arguments are handled. See xparse docs for details.
\IfBooleanTF{#1}%
{% We have a *.
E_{K{\IfValueT{#2}{\symup{,}#2}}}
}%
{% We don't have a *.
K_{\symup{trans}\IfValueT{#2}{\symup{,}#2}}
}%
}%
\begin{document}
\( \translationalkineticenergy \quad \translationalkineticenergy[\symup{final}]
\quad \translationalkineticenergy* \quad \translationalkineticenergy*[\symup{final}] \)
\end{document}
答案1
这里有两种简化方法。第一种是
\IfValueTF{#2}%
{%
E_{K{\textnormal{,}#2}}%
}%
{%
E_{K}%
}%
这两个分支的区别在于，如果true您有一个额外的{\textnormal{,}#2}，您可以将测试放在下标内：
E_{K%
\IfValueT{#2}{\textnormal{,}#2}%
}%
第二个有点棘手。您会看到，在 TeX 看到下标（或上标）标记后，括号{不必是显式括号：它可以是隐式括号，并且隐式括号不计入括号平衡。这两个都做同样的事情：
a_{bc}
a_\bgroup bc\egroup
因此您可以在宏中执行此操作：
\NewDocumentCommand{\translationalkineticenergy}{ s d[] }{%
% d[] must be used because of the way consecutive optional
% arguments are handled. See xparse docs for details.
\IfBooleanTF{#1}%
{E_\bgroup K}% We have a *.
{K_\bgroup \textnormal{trans}}% We don't have a *.
\IfValueT{#2}{\textnormal{,}#2}%
\egroup
}%
\bgroup请注意，其中有两个，但只有一个，这没问题，因为实际上只能看到\egroup其中一个。\bgroup