我的處境相當獨特。我想將命令輸出的部分“標記”為前綴或後綴。例如：
\newcommand{\L}[1]{L\postfix{_i}}
然後能夠做這樣的事情：
\newcommand{\est}[1]{\prefixof{#1}\hat{\mainbodyof{#1}}\postfixof{#1}}
理想情況下，這應該適用於普通文本，例如\est{\lambda}應該擴展到\hat{\lambda}.另外，\L應該擴展到L_i，並且\est{\L}應該擴展到\hat{L}_i。
我知道這對 TeX 是可能的（它是圖靈完備的），但我不知道從哪裡開始，或者除了macros.
看來@DavidCarlisle 的答案在這種情況下不起作用：
\documentclass{article}
\usepackage{etoolbox}
\newcommand\zzfix[3]{#1#2#3}%pre-main-post
\def\prefixof#1{\expandafter\zzpre#1\relax{#1}}
\def\postfixof#1{\expandafter\zzpost#1\relax{#1}}
\def\mainbodyof#1{\expandafter\zzmain#1\relax{#1}}
\def\zzpre#1{\ifx\zzfix#1\expandafter\oneoffive\else\expandafter\gobblepastrelax\fi}
\def\zzpost#1{\ifx\zzfix#1\expandafter\threeoffive\else\expandafter\gobblepastrelax\fi}
\def\zzmain#1{\ifx\zzfix#1\expandafter\twooffive\else\expandafter\afterrelax\fi}
\def\oneoffive#1#2#3\relax#4{#1}
\def\twooffive#1#2#3\relax#4{#2}
\def\threeoffive#1#2#3\relax#4{#3}
\def\afterrelax#1\relax#2{#2}
\def\gobblepastrelax#1\relax#2{}
\newcommand{\queueState}[1][]{\zzfix{}{\ell}{\ifstrempty{#1}{}{_{#1}}}}
\newcommand{\baseQuantity}[1]{\prefixof{#1}\bar{\mainbodyof{#1}}\postfixof{#1}}
\begin{document}
But this does not work: $\baseQuantity{\queueState[1:N]}$
\end{document}
也許也可以讓它發揮作用？
\show\queueState輸出：
> \queueState=macro:
->\@protected@testopt \queueState \\queueState {}.
答案1
\documentclass{article}
\newcommand\zzfix[3]{#1#2#3}%pre-main-post
\renewcommand{\L}{\zzfix{}{L}{_i}}
\newcommand{\est}[1]{\prefixof{#1}\hat{\mainbodyof{#1}}\postfixof{#1}}
\def\prefixof#1{\expandafter\zzpre#1\relax{#1}}
\def\postfixof#1{\expandafter\zzpost#1\relax{#1}}
\def\mainbodyof#1{\expandafter\zzmain#1\relax{#1}}
\def\zzpre#1{\ifx\zzfix#1\expandafter\oneoffive\else\expandafter\gobblepastrelax\fi}
\def\zzpost#1{\ifx\zzfix#1\expandafter\threeoffive\else\expandafter\gobblepastrelax\fi}
\def\zzmain#1{\ifx\zzfix#1\expandafter\twooffive\else\expandafter\afterrelax\fi}
\def\oneoffive#1#2#3\relax#4{#1}
\def\twooffive#1#2#3\relax#4{#2}
\def\threeoffive#1#2#3\relax#4{#3}
\def\afterrelax#1\relax#2{#2}
\def\gobblepastrelax#1\relax#2{}
\begin{document}
Ideally, this should work on normal text, e.g. $\est{\lambda}$ should
expand to $\hat{\lambda}$. Also, $\L$ should expand to $L_i$, and $\est{\L}$
should expand to $\hat{L}_i$.
\end{document}