如何测试（文本）数字的第一位和最后一位数字？

Question 1

只需引入可扩展的宏来获取字符串的第一位或最后一位数字。

\documentclass{article}
\usepackage{fontspec}

%\setmainfont{STIXTwoText-Regular}
%\newfontfamily\fracfigs{STIXTwoText-Medium}[% compensate weight for scaling
%  Numbers = {Proportional,Lining},
%  Scale   = 0.75]

% Actual kerns wrong for this font, but everyone will have it:
\setmainfont{Latin Modern Roman}
\newfontfamily\fracfigs{Latin Modern Roman}[Scale = 0.75]
\def\getfirst#1#2\relax{#1}
\def\getlast#1#2\relax{\if\relax#2\relax#1\else\getlast#2\relax\fi}

\newcommand*\myFii{2}
\newcommand*\myFiv{4}
\newcommand*\myFvi{6}
\newcommand*\myFvii{7}
\newcommand*\myFix{9}
\newcommand*\myfrac[2]{%
  \edef\myfractmpn{\getlast#1\relax}% Really want just last char
  \edef\myfractmpd{\getfirst#2\relax}% Really want just first char
  \raisebox{0.5ex}{{\fracfigs#1}}%
  \ifx\myfractmpn\myFii       \kern 0.1em%
  \else\ifx\myfractmpn\myFvii \kern -0.05em%
  \else\ifx\myfractmpn\myFix  \kern 0pt%
  \else                       \kern 0.05em%
  \fi\fi\fi%
  \textfractionsolidus%
  \ifx\myfractmpd\myFiv       \kern -0.05em%
  \else\ifx\myfractmpd\myFvi  \kern 0pt%
  \else                       \kern 0.05em%
  \fi\fi%
  {\fracfigs#2}}

\begin{document}
\myfrac{1}{1}\quad \myfrac{11}{11}\par
\myfrac{2}{2}\quad \myfrac{22}{22}\par
\myfrac{3}{3}\quad \myfrac{33}{33}\par
\myfrac{4}{4}\quad \myfrac{44}{44}\par
\myfrac{5}{5}\quad \myfrac{55}{55}\par
\myfrac{6}{6}\quad \myfrac{66}{66}\par
\myfrac{7}{7}\quad \myfrac{77}{77}\par
\myfrac{8}{8}\quad \myfrac{88}{88}\par
\myfrac{9}{9}\quad \myfrac{99}{99}\par
\end{document}

Answer

只需引入可扩展的宏来获取字符串的第一位或最后一位数字。

\documentclass{article}
\usepackage{fontspec}

%\setmainfont{STIXTwoText-Regular}
%\newfontfamily\fracfigs{STIXTwoText-Medium}[% compensate weight for scaling
%  Numbers = {Proportional,Lining},
%  Scale   = 0.75]

% Actual kerns wrong for this font, but everyone will have it:
\setmainfont{Latin Modern Roman}
\newfontfamily\fracfigs{Latin Modern Roman}[Scale = 0.75]
\def\getfirst#1#2\relax{#1}
\def\getlast#1#2\relax{\if\relax#2\relax#1\else\getlast#2\relax\fi}

\newcommand*\myFii{2}
\newcommand*\myFiv{4}
\newcommand*\myFvi{6}
\newcommand*\myFvii{7}
\newcommand*\myFix{9}
\newcommand*\myfrac[2]{%
  \edef\myfractmpn{\getlast#1\relax}% Really want just last char
  \edef\myfractmpd{\getfirst#2\relax}% Really want just first char
  \raisebox{0.5ex}{{\fracfigs#1}}%
  \ifx\myfractmpn\myFii       \kern 0.1em%
  \else\ifx\myfractmpn\myFvii \kern -0.05em%
  \else\ifx\myfractmpn\myFix  \kern 0pt%
  \else                       \kern 0.05em%
  \fi\fi\fi%
  \textfractionsolidus%
  \ifx\myfractmpd\myFiv       \kern -0.05em%
  \else\ifx\myfractmpd\myFvi  \kern 0pt%
  \else                       \kern 0.05em%
  \fi\fi%
  {\fracfigs#2}}

\begin{document}
\myfrac{1}{1}\quad \myfrac{11}{11}\par
\myfrac{2}{2}\quad \myfrac{22}{22}\par
\myfrac{3}{3}\quad \myfrac{33}{33}\par
\myfrac{4}{4}\quad \myfrac{44}{44}\par
\myfrac{5}{5}\quad \myfrac{55}{55}\par
\myfrac{6}{6}\quad \myfrac{66}{66}\par
\myfrac{7}{7}\quad \myfrac{77}{77}\par
\myfrac{8}{8}\quad \myfrac{88}{88}\par
\myfrac{9}{9}\quad \myfrac{99}{99}\par
\end{document}

Question 2

使用expl3；\tl_item:nn { #1 } { -1 }我们提取参数中的最后一项和\tl_item:nn { #2 } { 1 }第一项。

如何填写其他数字的字距应该很清楚。请注意，在第二次调用中，F“no match”参数用于插入默认字距 0.05em。

\documentclass{article}
\usepackage{fontspec}

\setmainfont{STIX Two Text}
\newfontface{\fracfigs}{STIXTwoText-Medium}[% compensate weight for scaling
  Extension=.otf,
  Numbers = Proportional,
  Scale   = 0.75,
]

\ExplSyntaxOn

\NewDocumentCommand{\myfrac}{mm}
 {
  \dedded_myfrac:nn { #1 } { #2 }
 }

\cs_new_protected:Nn \dedded_myfrac:nn
 {
  \raisebox{0.5ex}{\fracfigs #1}
  \str_case_e:nn { \tl_item:nn { #1 } { -1 } }
   {
    {2}{\kern 0.1em}
    {7}{\kern -0.05em}
    {9}{\kern 0.05em}
   }
  \textfractionsolidus
  \str_case_e:nnF { \tl_item:nn { #2 } { 1 } }
   {
    {4}{\kern 0.05em}
    {6}{}
   }
   {\kern 0.05em}
   {\fracfigs#2}
 }

\ExplSyntaxOff

\begin{document}

\myfrac{1}{1}\quad \myfrac{11}{11}\par
\myfrac{2}{2}\quad \myfrac{22}{22}\par
\myfrac{3}{3}\quad \myfrac{33}{33}\par
\myfrac{4}{4}\quad \myfrac{44}{44}\par
\myfrac{5}{5}\quad \myfrac{55}{55}\par
\myfrac{6}{6}\quad \myfrac{66}{66}\par
\myfrac{7}{7}\quad \myfrac{77}{77}\par
\myfrac{8}{8}\quad \myfrac{88}{88}\par
\myfrac{9}{9}\quad \myfrac{99}{99}\par

\end{document}

不管怎样，这样的分数都是丑陋的。

是什么\str_case_e:nnTF？_e部分表示参数在被“字符串化”之前要进行完全扩展，因此\tl_item:nn在检查字符串之前会进行评估。的第一个参数\str_case_e:nnTF是要测试的字符串；第二个参数应采用以下形式

{<str-1>}{<code for case-1>}
{<str-2>}{<code for case-2>}
...
{<str-n>}{<code for case-n>}

如果匹配，则插入相应的代码，然后插入第三个参数（）中的代码；如果不匹配，则插入T第四个参数（）的代码。F

然而，一个非常方便的expl3惯例是T和F参数是“特殊的”，所以我们实际上有四个完整的函数，即

\str_case_e:nn    \str_case_e:nnF    \str_case_e:nnT    \str_case_e:nnTF

最有用的是前两个

Answer