我想仅使用一个开关更改一些文档边距。但是，宏似乎没有被评估？！下面，我仅显示了应由一个变量控制的 3 个值中的 1 个。
\newcommand{\headsepValue}[3]{%
\IfEqCase{#1}{%
{a}{43mm}% \headsep{43mm}
{b}{53mm}% \headsep{53mm}
{c}{63mm}% \headsep{63mm}
% you can add more cases here as desired
}[\PackageError{headsepValue}{Undefined option to headsepValue: #1}{}]%
}%
\newcommand{\valueUsedForSpacing}{a}
\setlength{\headsep}{\headsepValue{\valueUsedForSpacing}}
这给了我一个错误（！缺少数字，视为零）。我必须以\expandafter某种方式使用吗？或者我如何告诉 Latex 我想要：
\setlength{\headsep}{\headsepValue{\valueUsedForSpacing}}
其计算结果应为
\setlength{\headsep}{\headsepValue{a}}
进而
\setlength{\headsep}{43mm}
感谢您的帮助！
更新：感谢到目前为止的所有回复！稍后我会仔细研究建议的替代方案。但首先我会向您提供我的代码。
我使用 g-brief 并尝试对其进行一些修改。我添加了example.tex和g-brief.cls，结果出现了错误。
这是 example.tex：
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% PREAMBLE %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\documentclass[english,10pt]{g-brief}
\renewcommand{\familydefault}{\sfdefault}
\newcommand*{\myfont}{\fontfamily{ptm}\selectfont} %font in header and footer ptm=Times
\usepackage{helvet}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{ifthen}
\usepackage{etoolbox}
\usepackage{pgfplots}
\pgfplotsset{compat=1.7}
\usetikzlibrary{fadings}
\lochermarke
\faltmarken
%\fenstermarken
\trennlinien
%\klassisch
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Body %
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
\Name{MyName}
\Strasse{MyAddress}
%\Zusatz{}
\Ort{MyPlace}
\Land{MyCountry}
\Telefon{MyPhoneNumber}
%\Telex{}
\EMail{MyEmail}
\HTTP{MyHTTP}
%\Bank{}
%\BLZ{}
%\Konto{}
\RetourAdresse{ } % Wichtig: Muss ein Leerzeichen sein, sonst gibt's
% Probleme mit dem Brief-Fenster, falls ein Land
% angegeben wird
\Adresse{YourName\\
YourAddress\\
YourCountry\\
}
\Datum{\today}
%\Postvermerk{}
%\MeinZeichen{}
\Betreff{Modify g-brief.cls}
%\IhrSchreiben{}
%\Anlagen{CV attached}
%\Verteiler{}
\Anrede{GreetingToYou,}
\Gruss{ByeBye}{0.2cm}
\Unterschrift{MySignature}
\begin{g-brief}
If I have lot of text here, I want to be able to adjust several margins to squeeze everything on one single page instead of ending up with e.g. a few words on the next page
Margins that I would like to change are: 1) separation between header and address field, 2) based on that change the available text height [and 3) should actually be the vertical position of the line separating the footer, which is linked to the text height]
\end{g-brief}
\end{document}
...这是我修改后的 g-brief.cls
%%
%% This is file `g-brief.cls',
%% generated with the docstrip utility.
%%
%% The original source files were:
%%
%% g-brief.dtx (with options: `class')
%%
%% =======================================================================
%%
%% Copyright (C) 1991-2003 Michael Lenzen.
%%
%% For additional copyright information see further down in this file.
%%
%% This file is part of the G-BRIEF package.
%% -----------------------------------------------------------------------
%%
%% It may be distributed under the terms of the LaTeX Project Public
%% License (LPPL), as described in lppl.txt in the base LaTeX distribution.
%% Either version 1.1 or, at your option, any later version.
%%
%% The latest version of this license is in
%%
%% http://www.latex-project.org/lppl.txt
%%
%% LPPL Version 1.1 or later is part of all distributions of LaTeX
%% version 1999/06/01 or later.
%%
%%
%% Error reports in case of UNCHANGED versions to
%%
%% <[email protected]>
%% <[email protected]>
%%
%%
\usepackage{xstring}
\def\filedate{2008/07/15}
\def\fileversion{4.0.2}
\def\filedate{2008/07/15}
\def\fileversion{4.0.2}
\def\filename{g-brief.cls}
\NeedsTeXFormat{LaTeX2e}[2001/06/01]
\ProvidesClass{g-brief}[\filedate\space v\fileversion\space g-brief class]
\newdimen\VorschubH
\newdimen\VorschubV
\VorschubH = 0.0mm
\VorschubV = 0.0mm
\def\sprache{ngerman}
\def\telefontex{{\footnotesize Telefon\/:}}
\def\telefaxtext{{\footnotesize Telefax\/:}}
\def\telextext{{\footnotesize Telex\/:}}
\def\emailtext{{\footnotesize e--Mail\/:}}
\def\httptext{{\footnotesize HTTP\/:}}
\def\banktext{{\footnotesize Bankverbindung\/:}}
\def\blztext{{\footnotesize BLZ\/:}}
\def\kontotext{{\footnotesize Kto.\/:}}
\def\betrefftext{{\normalsize Betreff\/:}}
\def\ihrzeichentext{\footnotesize\textsc{Ihr Zeichen}}
\def\ihrschreibentext{\footnotesize\textsc{Ihr Schreiben vom}}
\def\meinzeichentext{\footnotesize\textsc{Mein Zeichen}}
\def\unserzeichentext{\footnotesize\textsc{Unser Zeichen}}
\def\datumtext{\footnotesize\textsc{Datum}}
\def\datum{\number\day.~\ifcase\month\or Januar\or Februar\or
M\"arz\or April\or Mai\or Juni\or Juli\or August\or September\or
Oktober\or November\or Dezember\fi \space\number\year}
\DeclareOption{english}{
\def\sprache{english}
\def\telefontex{{\footnotesize Phone\/:}}
\def\telefaxtext{{\footnotesize Fax\/:}}
\def\telextext{{\footnotesize Telex\/:}}
\def\emailtext{{\footnotesize e--Mail\/:}}
\def\httptext{{\footnotesize HTTP\/:}}
\def\banktext{{\footnotesize Bank\/:}} \def\blztext{{\footnotesize
code}} \def\kontotext{{\footnotesize acct}}
\def\betrefftext{{\normalsize Subject:}}
\def\ihrzeichentext{\footnotesize\textsc{Your Ref.}}
\def\ihrschreibentext{\footnotesize\textsc{Your Mail}}
\def\meinzeichentext{\footnotesize\textsc{My Ref.}}
\def\unserzeichentext{\footnotesize\textsc{Our Ref.}}
\def\datumtext{\footnotesize\textsc{Date}}
}
\DeclareOption{american}{
\def\sprache{american}
\def\telefontex{{\footnotesize Phone\/:}}
\def\telefaxtext{{\footnotesize Fax\/:}}
\def\telextext{{\footnotesize Telex\/:}}
\def\emailtext{{\footnotesize e--Mail\/:}}
\def\httptext{{\footnotesize HTTP\/:}}
\def\banktext{{\footnotesize Bank\/:}} \def\blztext{{\footnotesize
code}} \def\kontotext{{\footnotesize acct}}
\def\betrefftext{{\normalsize Subject:}}
\def\ihrzeichentext{\footnotesize\textsc{Your Ref.}}
\def\ihrschreibentext{\footnotesize\textsc{Your Mail}}
\def\meinzeichentext{\footnotesize\textsc{My Ref.}}
\def\unserzeichentext{\footnotesize\textsc{Our Ref.}}
\def\datumtext{\footnotesize\textsc{Date}}
}
\DeclareOption{10pt}{\def\@schrift{0}}
\DeclareOption{11pt}{\def\@schrift{1}}
\DeclareOption{12pt}{\def\@schrift{2}}
\let\@docencoding\@empty
\DeclareOption{ansinew}{\def\@docencoding{ansinew}}
\DeclareOption{applemac}{\def\@docencoding{applemac}}
\DeclareOption{ascii}{\def\@docencoding{ascii}}
\DeclareOption{cp1250}{\def\@docencoding{cp1250}}
\DeclareOption{cp1252}{\def\@docencoding{cp1252}}
\DeclareOption{cp437de}{\def\@docencoding{cp437de}}
\DeclareOption{cp437}{\def\@docencoding{cp437}}
\DeclareOption{cp850}{\def\@docencoding{cp850}}
\DeclareOption{cp852}{\def\@docencoding{cp852}}
\DeclareOption{cp865}{\def\@docencoding{cp865}}
\DeclareOption{decmulti}{\def\@docencoding{decmulti}}
\DeclareOption{latin1}{\def\@docencoding{latin1}}
\DeclareOption{latin2}{\def\@docencoding{latin2}}
\DeclareOption{latin3}{\def\@docencoding{latin3}}
\DeclareOption{latin4}{\def\@docencoding{latin4}}
\DeclareOption{latin5}{\def\@docencoding{latin5}}
\DeclareOption{latin9}{\def\@docencoding{latin9}}
\DeclareOption{next}{\def\@docencoding{next}}
\ExecuteOptions{11pt,@sprache} \ProcessOptions
\LoadClass[1\@schrift pt, a4paper, oneside, final]{letter}[1999/04/29]
\normalsize
\newcommand{\headsepValue}[3]{%
\IfEqCase{#1}{%
{a}{43mm}% \headsep{43mm}
{b}{53mm}% \headsep{53mm}
{c}{63mm}% \headsep{63mm}
% you can add more cases here as desired
}[\PackageError{headsepValue}{Undefined option to headsepValue: #1}{}]%
}%
\newcommand{\txtHeight}[3]{%
\IfStrEqCase{#1}{%
{a}{208.88mm}% \headsep{43mm}
{b}{198.88mm}% \headsep{53mm}
{c}{188.88mm}% \headsep{63mm}
% you can add more cases here as desired
}[\PackageError{txtHeight}{Undefined option to txtHeight: #1}{}]%
}%
\newcommand{\yPosition}[3]{%
\IfStrEqCase{#1}{%
{a}{-770pt}% \headsep{43mm}
{b}{-760pt}% \headsep{53mm}
{c}{-750pt}% \headsep{63mm}
% you can add more cases here as desired
}[\PackageError{yPosition}{Undefined option to yPosition: #1}{}]%
}%
\newcommand{\valueUsedForSpacing}{a}
\setlength\oddsidemargin{0\p@}
\setlength\evensidemargin{\oddsidemargin}
\setlength\marginparwidth{90\p@}
\setlength\marginparsep{11\p@}
\setlength\marginparpush{5\p@}
\setlength\topmargin{-12.69mm}
\setlength\headheight{4.23mm}
%\setlength{\headsep}{43mm} % 43mm=a,(53mm=b),63mm=c;
\setlength{\headsep}{\headsepValue{\valueUsedForSpacing}}
\setlength\topskip{3.38mm}
\addtolength\footskip{4.23mm}
\setlength\textheight{208.88mm} %43mm=208.88mm,(53mm=198.88mm),63mm = 188.88mm
\setlength\textwidth{165mm}
\setlength\lineskip{1\p@}
\setlength\normallineskip{1\p@}
\renewcommand\baselinestretch{1}
\advance\topmargin by \VorschubV
\advance\oddsidemargin by \VorschubH
\setlength\evensidemargin{\oddsidemargin}
\AtEndOfClass{\pagestyle{regularpage}}
\def\Name#1{\def\name{#1}} \def\name{}
\def\Strasse#1{\def\strasse{#1}} \def\strasse{}
\def\Zusatz#1{\def\zusatz{#1}} \def\zusatz{}
\def\Ort#1{\def\ort{#1}} \def\ort{}
\def\Land#1{\def\land{#1}} \def\land{}
\def\RetourAdresse#1{\def\retouradresse{#1}} \def\retouradresse{}
\def\Telefax#1{\def\telefax{#1}} \def\telefax{}
\def\Telex#1{\def\telex{#1}} \def\telex{}
\def\EMail#1{\def\email{#1}} \def\email{}
\def\HTTP#1{\def\http{#1}} \def\http{}
\def\Bank#1{\def\bank{#1}} \def\bank{}
\def\BLZ#1{\def\blz{#1}} \def\blz{}
\def\Konto#1{\def\konto{#1}} \def\konto{}
\def\Postvermerk#1{\def\postvermerk{#1}} \def\postvermerk{}
\def\Adresse#1{\def\adresse{#1}} \def\adresse{}
\def\IhrZeichen#1{\def\ihrzeichen{#1}} \def\ihrzeichen{}
\def\IhrSchreiben#1{\def\ihrschreiben{#1}} \def\ihrschreiben{}
\def\MeinZeichen#1{\def\meinzeichen{#1}} \def\meinzeichen{}
\def\Datum#1{\def\datum{#1}} \def\datum{\today}
\def\Betreff#1{\def\betreff{#1}} \def\betreff{}
\def\Anrede#1{\def\anrede{#1}} \def\anrede{}
\def\Gruss#1#2{\def\gruss{#1} \def\grussskip{#2}}
\def\gruss{}
\def\grussskip{}
\def\Unterschrift#1{\def\unterschrift{#1}} \def\unterschrift{}
\def\Anlagen#1{\def\anlagen{#1}} \def\anlagen{}
\def\Verteiler#1{\def\verteiler{#1}} \def\verteiler{}
\long\def\Einrueckung#1{\par\begin{tabular}{@{\hspace{1in}}p{5in}@{}}
#1\end{tabular}\par}
\newif\ifklassisch\klassischfalse
\def\klassisch{\klassischtrue}
\newif\iftrennlinien\trennlinienfalse
\def\trennlinien{\trennlinientrue}
\newif\iflochermarke\lochermarkefalse
\def\lochermarke{\lochermarketrue}
\newif\iffaltmarken\faltmarkenfalse
\def\faltmarken{\faltmarkentrue}
\newif\iffenstermarken\fenstermarkenfalse
\def\fenstermarken{\fenstermarkentrue}
\newif\ifunserzeichen\unserzeichenfalse
\def\unserzeichen{\unserzeichentrue}
\newenvironment{g-brief}{
\thispagestyle{firstpage}
\setlength\unitlength{1mm}
\c@page\@ne
\interlinepenalty=200
\clearpage
\ifx \ihrzeichen\empty \ifx \ihrschreiben\empty \ifx
\meinzeichen\empty \makebox[50.5mm][l]{} \makebox[55.0mm][l]{}
\makebox[20.0mm][l]{} \else \makebox[45.5mm][l]{\ihrzeichentext}
\makebox[55.0mm][l]{\ihrschreibentext} \ifunserzeichen
\makebox[20.0mm][l]{\unserzeichentext} \else
\makebox[20.0mm][l]{\meinzeichentext} \fi \fi \else
\makebox[45.5mm][l]{\ihrzeichentext}
\makebox[55.0mm][l]{\ihrschreibentext} \ifunserzeichen
\makebox[20.0mm][l]{\unserzeichentext} \else
\makebox[20.0mm][l]{\meinzeichentext} \fi \fi \else
\makebox[45.5mm][l]{\ihrzeichentext}
\makebox[55.0mm][l]{\ihrschreibentext} \ifunserzeichen
\makebox[20.0mm][l]{\unserzeichentext} \else
\makebox[20.0mm][l]{\meinzeichentext} \fi \fi
\makebox[37.0mm][r]{\datumtext} \\
\makebox[45.5mm][l]{\ihrzeichen}
\makebox[55.0mm][l]{\ihrschreiben}
\makebox[20.0mm][l]{\meinzeichen}
\makebox[42.0mm][r]{\datum} \par
\vspace{8mm}
\ifcase\@ptsize\vspace{0.045pt}\or \vspace{-1.555pt}\or
\vspace{-2.955pt} \fi
\ifx \betreff\empty
\else \ifklassisch
\betrefftext \space \space \betreff
\else
\textbf{\betreff}
\fi
\mbox{} \par \vspace{-1\parskip} \vspace{8mm}
\fi
\ifcase\@ptsize\vspace{0.045pt}\or \vspace{-1.555pt}\or
\vspace{-2.955pt} \fi
\ifx \anrede\empty \else \anrede \par \fi\nobreak
\addtolength\textheight{63mm}
}
{
\renewcommand{\baselinestretch}{1.0}
\ifcase \@ptsize\relax \normalsize \or \small \or \footnotesize \fi
\vspace{\grussskip} \par \nobreak \stopbreaks \noindent
\parbox[t]{3.5in}{\raggedright \ignorespaces {\normalsize \ifx
\gruss\empty \else \gruss \mbox{} \\[13.92mm] \fi \ifx
\unterschrift\empty \relax \else \ifklassisch
\textsl{(\unterschrift)} \else \unterschrift \fi
\fi}\strut} \ifx \anlagen\empty \else \vspace{4mm} \par \anlagen
\par \fi \ifx \verteiler\empty \else \ifx \anlagen\empty
\vspace{4mm}\par \fi \verteiler \fi }
\def\ps@firstpage{
\renewcommand{\baselinestretch}{1.0}
\ifcase \@ptsize\relax \normalsize \or \small \or \footnotesize \fi
\headheight16pt
\def\@oddhead{
\unitlength1mm
\begin{picture}(0,0)
\put(-9, 3){\parbox{180mm}{\Large \myfont \ifklassisch \textsl{\quad\name}
\else \textsc{\quad\name} \fi}}
\put(-9, 4){\parbox{180mm}{\hfill \normalsize \myfont \ifklassisch \textsl{
\begin{tabular}{r} \strasse \quad \\ \ifx \zusatz\empty \else
\zusatz \quad \\ \fi \ort \quad \ifx \land\empty \else \\
\land \quad \fi \end{tabular}} \else \textsc{
\begin{tabular}{r} \strasse \quad \\ \ifx \zusatz\empty \else
\zusatz \quad \\ \fi \ort \quad \ifx \land\empty \else \\
\land \quad \fi \end{tabular}} \fi }}
\iftrennlinien
\begin{tikzpicture}[remember picture,overlay]
\path[left color=white,right color=white,middle color=black]
([xshift=45pt,yshift=-70pt]current page.north west)+(0,0) rectangle +(185mm,0.5pt);
\end{tikzpicture}
\fi
\iflochermarke \put(-20,- 130.50){\line(1,0){4}} \fi
\iffaltmarken \put(-15,- 75.16){\line(1,0){3}}
\put(-15,-182.16){\line(1,0){3}} \fi
\put( -9, -22.00){\makebox(85,4) %-22
{\scriptsize \ifx \retouradresse\empty
\textrm{\name\ $\cdot$\ \strasse\ $\cdot$\ \ort \ifx
\land\empty \else \ $\cdot$\ \land \fi } \else
\textrm{} \fi}}
\put(-1,-28.15){\parbox[t]{4in}{\ifx \postvermerk\empty \hfill \par
\else \textbf{\postvermerk} \par \vspace{2mm} \fi \adresse}}
\iffenstermarken
\put(-9,-18.15){\line( 1, 0){1}} \put(-9,-18.15){\line( 0,-1){1}}
\put(76,-18.15){\line(-1, 0){1}} \put(76,-18.15){\line( 0,-1){1}}
\put(-9,-61.00){\line( 1, 0){1}} \put(-9,-61.00){\line( 0, 1){1}}
\put(76,-61.00){\line(-1, 0){1}} \put(76,-61.00){\line( 0, 1){1}}
\fi
\end{picture}
\hfill}
\def\@oddfoot{\unitlength1mm
\begin{picture}(0,0)
\put(-9,0){\parbox{180mm}{\footnotesize \myfont
\iftrennlinien %trennlinie footer
\begin{tikzpicture}[remember picture,overlay]
%\if \headsep43mm -790pt \else \if \headsep53mm -780pt \else -770pt \fi \fi
%\if\headsep43mm -790pt\fi \if\headsep53mm -780pt\fi \if\headsep63mm -770pt\fi
\path[left color=white,right color=white,middle color=black]
([xshift=45pt,yshift= \if \headsep43mm -790pt \else -780pt \fi ]current page.north west)+(0,0) rectangle +(185mm,0.5pt);
\end{tikzpicture}
\fi
\begin{tabular}{ll}
\ifx \telefon\empty \else \telefontex & \telefon \\ \fi \ifx
\telefax\empty \else \telefaxtext & \telefax \\ \fi \ifx
\telex\empty \else \telextext & \telex \\ \fi \ifx
\email\empty \else \emailtext & \email \\ \fi \ifx
\http\empty \else \httptext & \http \\ \fi \
\end{tabular}\hfill
\begin{tabular}{ll}
\ifx \bank\empty \else \ifx \blz\empty \else \ifx
\konto\empty \else \banktext & \bank \\ & \blztext \space \blz
\\ & \kontotext \space \konto \\ \ \fi \fi \fi
\end{tabular}}}
\end{picture} \hfill}
\def\@evenhead{\@oddhead} \def\@evenfoot{\@oddfoot}}
\def\ps@regularpage{ \headheight36pt\def\@oddhead{\unitlength1mm
\begin{picture}(0,0)
\put(-9,3){\makebox(180,15){\normalsize \ifklassisch \textsl{
{\Large\quad}\name\hfill\datum\hfill\pagename\ \thepage\quad}
\else \textsc{{\Large\quad}\name\hfill\datum\hfill\pagename\
\thepage\quad} \fi}}
\if \put(-9,0){\rule{180mm}{0.5pt}} \fi
\end{picture}\hfill}
\def\@oddfoot{\empty} \def\@evenhead{\@oddhead}
\def\@evenfoot{\@oddfoot}}
\IfFileExists{babel.sty}
{\RequirePackage[\sprache]{babel}[2001/03/01]}
{\ClassError{g-brief}
{Babel not installed !!!}
{Get babel package !!!}}
\ifx \@docencoding\empty \else
\IfFileExists{inputenc.sty}
{\RequirePackage[\@docencoding]{inputenc}}
{\ClassError{g-brief}
{LaTeX2e not complete installed or out of date !!!}
{Get current LaTeX2e !!!}}
\fi
\IfFileExists{marvosym.sty}
{\RequirePackage{marvosym}}
{}
\def\Telefon#1{\def\telefon{#1}} \def\telefon{}
\IfFileExists{europs.sty}
{\RequirePackage{europs}}
{}{}
\IfFileExists{eurosym.sty}
{\RequirePackage{eurosym}}
{}{}
\endinput
%%
%% End of file `g-brief.cls'.
更新 2：谢谢大家！我选择了最简单的解决方案，\ifcase成功了！
答案1
宏\IfEqCase返回在案例中进行选择的指令，并印刷结果。它不能在您希望的上下文中使用，因为它\setlength需要明确的长度，而不是生成它的指令。
您需要一个可扩展的版本：
\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\setvalues}{mmm}
{ % #1 = symbolic name, #2 = set of values, #3 = default for error
\cs_new:Npn #1 ##1
{
\str_case_x:nnF { ##1 }{ #2 }
{% invalid case
#3
\msg_error:nnn{sam-oht/setvalues}{invalid}{##1}
}
}
}
\msg_new:nnnn{sam-oht/setvalues}{invalid}
{
Invalid~choice~'#1'
}
{
You~have~to~supply~a~good~value,~not~'#1'
}
\ExplSyntaxOff
\setvalues{\headsepValue}{
{a}{43mm}% \headsep{43mm}
{b}{53mm}% \headsep{53mm}
{c}{63mm}% \headsep{63mm}
}{0pt}
\begin{document}
\newcommand{\valueUsedForSpacing}{a}
\setlength{\headsep}{\headsepValue{\valueUsedForSpacing}}
\the\headsep
\setlength{\headsep}{\headsepValue{c}}
\the\headsep
\setlength{\headsep}{\headsepValue{z}}
\the\headsep
\end{document}
这是控制台上的错误消息
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!
! sam-oht/setvalues error: "invalid"
!
! Invalid choice 'z'
!
! See the sam-oht/setvalues documentation for further information.
!
! For immediate help type H <return>.
!...............................................
l.43 \setlength{\headsep}{\headsepValue{z}}
? h
|'''''''''''''''''''''''''''''''''''''''''''''''
| You have to supply a good value, not 'z'
|...............................................
?
答案2
下面是一个示例，仅使用 eTeX 原语即可完成此操作：
\newdimen\headsep
\def\headsepvalue#1{\ifcase\numexpr`#1-`a\relax
43mm\or
53mm\or
63mm\else
0mm\errmessage{Undefined option to headsepvalue: #1}\fi
}
\headsep=\headsepvalue a
\message{\the\headsep} % test of value setting
\end
请注意，\ifcase原始是可扩展的。你不需要类似的东西\ExplSyntaxOn。