来自 TeXbook 第 11 章的排版字形框

Question

我试过 TeXbook 中的一个例子，但我不明白 Knuth 所说的内容：请参阅下面的代码片段。我应该得到一些矩形，但我得到的是对齐的文本，其中的字母与源代码中输入的字母完全相同。我在这里做错了什么？

Answer 1

以下内容摘自TeXbook 代码并转化为一个最小示例。为了避免影响其他类似列表的环境，我将其放在一个有限范围的组中 ( \begingroup... \endgroup)：

\documentclass{article}

\begin{document}

\begingroup

\def\dolist{\afterassignment\dodolist\let\next= }
\def\dodolist{\ifx\next\endlist \let\next\relax
  \else \\\let\next\dolist \fi
  \next}
\def\endlist{\endlist}
\def\hidehrule#1#2{\kern-#1%
  \hrule height#1 depth#2 \kern-#2 }
\def\hidevrule#1#2{\kern-#1{\dimen0=#1
    \advance\dimen0 by#2\vrule width\dimen0}\kern-#2 }
\def\makeblankbox#1#2{\hbox{\lower\dp0\vbox{\hidehrule{#1}{#2}%
    \kern-#1 % overlap the rules at the corners
    \hbox to \wd0{\hidevrule{#1}{#2}%
      \raise\ht0\vbox to #1{}% set the vrule height
      \lower\dp0\vtop to #1{}% set the vrule depth
      \hfil\hidevrule{#2}{#1}}%
    \kern-#1\hidehrule{#2}{#1}}}}
\def\maketypebox{\makeblankbox{0pt}{1pt}}
\def\makelightbox{\makeblankbox{.2pt}{.2pt}}
\def\\{\if\space\next\ % assume that \next is unexpandable
 \else \setbox0=\hbox{\next}\maketypebox\fi}
\def\demobox#1{\setbox0=\hbox{\dolist#1\endlist}%
  \leavevmode\copy0\kern-\wd0\makelightbox}

Q: Construct a \verb|\demobox| macro for use in writing manuals
like this, so that an author can write `\verb|\demobox{Tough exercise.}|'
in order to typeset `\thinspace\demobox{Tough exercise.}\thinspace'.

A: The following solution is based on a general \verb|\makeblankbox|
macro that prints the edges of a box using rules of given thickness
outside and inside that box; the box dimensions are those of\/ \verb|\box0|.

\endgroup

\begin{verbatim}
\def\dolist{\afterassignment\dodolist\let\next= }
\def\dodolist{\ifx\next\endlist \let\next\relax
  \else \\\let\next\dolist \fi
  \next}
\def\endlist{\endlist}
\def\hidehrule#1#2{\kern-#1%
  \hrule height#1 depth#2 \kern-#2 }
\def\hidevrule#1#2{\kern-#1{\dimen0=#1
    \advance\dimen0 by#2\vrule width\dimen0}\kern-#2 }
\def\makeblankbox#1#2{\hbox{\lower\dp0\vbox{\hidehrule{#1}{#2}%
    \kern-#1 % overlap the rules at the corners
    \hbox to \wd0{\hidevrule{#1}{#2}%
      \raise\ht0\vbox to #1{}% set the vrule height
      \lower\dp0\vtop to #1{}% set the vrule depth
      \hfil\hidevrule{#2}{#1}}%
    \kern-#1\hidehrule{#2}{#1}}}}
\def\maketypebox{\makeblankbox{0pt}{1pt}}
\def\makelightbox{\makeblankbox{.2pt}{.2pt}}
\def\\{\if\space\next\ % assume that \next is unexpandable
 \else \setbox0=\hbox{\next}\maketypebox\fi}
\def\demobox#1{\setbox0=\hbox{\dolist#1\endlist}%
  \leavevmode\copy0\kern-\wd0\makelightbox}
\end{verbatim}

\end{document}

您可以编写类似的\demoletter{<letter>}宏来将其内容放入框中而不打印它：

\newcommand{\demoletter}[1]{{\setlength{\fboxsep}{-\fboxrule}\fbox{\phantom{#1}}}}

\demoletter{O}\demoletter{n}\demoletter{e}
\demoletter{l}\demoletter{i}\demoletter{n}\demoletter{e}\demoletter{.}

Answer 2

该特定部分的代码TeXbook内容如下：

For example, you can say
\begintt
\vbox{\hbox{Two lines}\hbox{of type.}}
\endtt
and \TeX\ will convert this into
\begindisplay%
  \setbox0=\vbox{\hbox{\demobox{Two lines}}\hbox{\demobox{of type.}}}
$\vcenter{\hbox{\makelightbox\kern-\wd0\box0}}$\qquad
  i.e.,\qquad$\vcenter{\vbox{\hbox{Two lines}\hbox{of type.}}}$
\enddisplay

所以你可以看到 Knuth 告诉你输入：

\vbox{\hbox{Two lines}\hbox{of type.}}

但实际上他输入的是：

\vbox{\hbox{\demobox{Two lines}}\hbox{\demobox{of type.}}}

在练习 11.5 中，Knuth 建议你自己构建\demobox宏（当然，我不会在这里展示 :-)。构建完成后，你可以像这样使用它：

\vbox{%
  \hbox{\demobox{Go try to solve}}%
  \hbox{\demobox{Exercise 11.5}}%
  \hbox{\demobox{by yourself :-)}}%
}