如何应用 \ifthenelse 检查通过宏访问的列表成员？

Question

您好，提前谢谢您！

我正在尝试\ifthenelse对一个元素进行检查，该元素是使用找到的宏从列表中提取出来的这里。不幸的是，我不知道该怎么做：Undefined control sequence在尝试进行检查时抛出。扩展可能是问题所在，但这超出了我的知识范围。MWE：

\documentclass{minimal}
\usepackage{ifthen,tikz,xstring}
\usetikzlibrary{calc}

% define check
\newcommand{\checkValue}[1]{\ifthenelse{\equal{#1}{1}}{#1: true}{#1: false}}

% routine to extract list member
\newcommand*{\getListMember}[2]{%
    \edef\dotheloop{%
        \noexpand\foreach \noexpand\a [count=\noexpand\i] in {#1} {%
            \noexpand\IfEq{\noexpand\i}{#2}{\noexpand\a\noexpand\breakforeach}{}%
    }}%
    \dotheloop
}

\begin{document}
\noindent
\checkValue{0}\\    % works
\checkValue{1}\\    % works

\noindent
\def\theItem{\getListMember{0,1}{1}}%
Member to check: \theItem\\
Do check: %\checkValue{\theItem}    % fails: Undefined control sequence.
\end{document}

Answer 1

这些是扩展问题，但由于您正在加载 Ti钾Z：为什么你不直接使用内置的提取机制？

\documentclass{article}
\usepackage{ifthen,tikz,xstring}
\usetikzlibrary{calc}

% define check
\newcommand{\checkValue}[1]{\ifthenelse{\equal{#1}{1}}{#1: true}{#1: false}}


% routine to extract list member
\newcommand*{\getListMemberPgf}[3]{%
    \pgfmathsetmacro{#1}{{#2}[\the\numexpr#3-1]}%
}

\begin{document}
\noindent
\checkValue{0}\\    % works
\checkValue{1}\\    % works

\noindent
\getListMemberPgf{\theItem}{0,1}{1}%
Member to check: \theItem\\
Do check: \checkValue{\theItem}    %  no longer fails.
\end{document}

请注意，如果列表不仅包含数字，则需要将项目包装在其中"..."。

Answer 2

您可以使用xparse，它具有以下功能：可扩展从逗号分隔的值列表中提取项目。

您只需要注意expl3列表是从一开始索引的事实（这解释了+1第二个参数中的\clist_item:nn）。

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewExpandableDocumentCommand{\getListMember}{mm}
 {% #1 = clist, #2 = index
  \clist_item:nn { #1 } { #2+1 }
 }
\NewDocumentCommand{\saveListMember}{mmm}
 {% #1 = clist, #2 = index, #3 = macro
  \tl_if_exist:NF #1
   {
    \tl_new:N #1
    \tl_set:Nx #3 { \clist_item:nn { #1 } { #2+1 } }
   }
 }
\NewExpandableDocumentCommand{\checkValue}{m}
 {
  \str_if_eq:eeTF { #1 } { 1 } {#1:~true} {#1:~false}
 }
\ExplSyntaxOff

\begin{document}

\noindent
\checkValue{0}\\  % works
\checkValue{1}    % works

% directly access the member
\noindent
Member to check: \getListMember{0,1}{1}\\
Do check: \checkValue{\getListMember{0,1}{1}}

% alternative, saving the member in a control sequence
\saveListMember{0,1}{1}{\theItem}

\noindent
Member to check: \theItem\\
Do check: \checkValue{\theItem}

\end{document}