foreach 循环中的宏定义错误

Question

当我定义 \pluse 宏并在 foreach 循环中使用它时，报告错误：代码：

\documentclass[]{standalone}
 \usepackage{tikz}
 \usetikzlibrary{intersections}
 \begin{document}
 \begin{tikzpicture}
 \def\r{2}
 \def\plus{+(0.1,0) -- +(0.2,0.1) -- +(0.3,-0.1) -- +(0.4,0)}
 \coordinate (O) at (0,0);
 \draw[red,semithick,dashed,name path=arcafter] 
 (O) ++(\r,0) arc(0:-180:\r);
 \foreach \y in {0,...,4}
 {
      \draw[semithick,->,>=latex,name path=arrow] 
          (-\r,-\y*\r/4) -- (\r,-\y*\r/4);
      \draw[name intersections={
            of=arcafter and arrow,
            name=M,
            total=\t}] 
      foreach \i in {1,...,\t} 
      {
            (M-\i) ++(-0.2,0) \pluse
      };
 }
 \end{tikzpicture}
 \end{document}

错误信息：

! Undefined control sequence.
\@next ... \tikz@scan@next@command \pgf@let@token 

l.23  }

? 

如果用实际代码替换 \pluse，它就可以正常工作。不确定我的宏是否有问题！

Answer 1

您的代码很好。只有一个拼写错误。您定义了\plus但使用了\pluse。

\documentclass[tikz,border=3.14mm]{standalone}
\usetikzlibrary{intersections}
\begin{document}
\begin{tikzpicture}
 \def\r{2}
 \def\pluse{+(0.1,0) -- +(0.2,0.1) -- +(0.3,-0.1) -- +(0.4,0)}
 \coordinate (O) at (0,0);
 \draw[red,semithick,dashed,name path=arcafter] 
 (O) ++(\r,0) arc(0:-180:\r);
 \foreach \y in {0,...,4}
 {
      \draw[semithick,->,>=latex,name path=arrow] 
          (-\r,-\y*\r/4) -- (\r,-\y*\r/4);
      \draw[name intersections={
            of=arcafter and arrow,
            name=M,
            total=\t}] 
      foreach \i in {1,...,\t} 
      {
            (M-\i) ++(-0.2,0) \pluse
      };
 }
\end{tikzpicture}
\end{document}