我有以下宏
\usepackage{xintexpr}
\newcommand\seq[4] %length, delimiter, generating func, last term
{%
\def\s##1{\def\n{##1} #3}
\xintListWithSep{#2}
{%
\xintApply{\s}{\xintSeq{1}{#1}}
}%
#2\ldots
\ifx\\#4\\ %if 4th arg empty
%empty
\else
#2#4
\fi
}
该类型设置具有给定生成函数的序列,即
$\seq{3}{,}{\n}{n}$
$\seq{4}{,}{\n}{}$
$\seq{3}{,}{\sqrt{\n}}{}$
$\seq{3}{/}{\frac{1}{\n}}{\frac{1}{n}}$
相当于
$1, 2, 3, ..., n$
$1, 2, 3, 4, ...$
$\sqrt{1}, \sqrt{2}, \sqrt{3}, ...$
$\frac{1}{1}/ \frac{1}{2}/ \frac{1}{3}/ .../ \frac{1}{n}$
尽管它可以按预期工作,但是当它处于支持对齐的环境中并传递对齐制表符(&
)作为第二个参数并且第四个参数为空时,它会失败,即
\begin{align}
\seq{3}{&&,}{\n}{n} % this works
\seq{3}{&&,}{\n}{} % this causes an error
\end{align}
在修改了代码之后,我得出结论,错误是由语句\ifx
仅在评估字符%empty
并以字符开头时引起的,如下例所示:
\documentclass{article}
\usepackage{amsmath}
\newcommand\testa[2]
{%
\ifx\\#2\\
%empty, evaluation causes error
\else
#1
\fi
}
\newcommand\testb[2]
{%
\ifx\\#2\\
#1
\else
%full, evaluation causes error
\fi
}
\begin{document}
\begin{align}
\testa{&}{n} \\ %ok
\testb{&}{} \\ %ok
%
\testa{&}{} \\ %ok
\testb{&}{n} \\ %ok
%
foo\testa{&}{n} \\ %ok
foo\testb{&}{} \\ %ok
%
foo\testa{&}{} \\ % causes error
foo\testb{&}{n} % causes error
\end{align}
\end{document}
如何改变条件来处理对齐制表符?
如果问题太具体,请告诉我,我会删除它。
编辑:添加\usepackage{amsmath}
到示例中
答案1
您需要隐藏&
被跳过的分支
\documentclass{article}
\usepackage{amsmath}
\def\useone#1{#1}
\newcommand\testa[2]
{%
\ifx\\#2\\%%
%empty, evaluation causes error
\else
\useone{#1}%%
\fi
}
\newcommand\testb[2]
{%
\ifx\\#2\\%%
\useone{#1}%%
\else
%full, evaluation causes error
\fi
}
\begin{document}
\begin{align}
\testa{&}{n} \\ %ok
\testb{&}{} \\ %ok
%
\testa{&}{} \\ %ok
\testb{&}{n} \\ %ok
%
foo\testa{&}{n} \\ %ok
foo\testb{&}{} \\ %ok
%
foo\testa{&}{} \\ % causes error
foo\testb{&}{n} % causes error
\end{align}
\end{document}