Typeset dots around numbers (old typography)

\input expl3-generic % just for not using ConTeXt

\ExplSyntaxOn
\cs_set_eq:NN \dorecurse \prg_replicate:nn
\ExplSyntaxOff

\def\num#1{\unskip\adddot#1\adddot\ignorespaces}
\def\adddot{%
  \cleaders\hbox to 1.5\dimexpr\fontdimen2\font-\fontdimen4\font\relax{\hss.\hss}%
  \hskip1.5\fontdimen2\font plus \fontdimen3\font minus \fontdimen4\font
}

\dorecurse{100}{The \num{2} element \num{2} xy. }

\bye

enter image description here

If the period should be attached to the number, it's even simpler.

\input expl3-generic

\ExplSyntaxOn
\cs_set_eq:NN \dorecurse \prg_replicate:nn
\ExplSyntaxOff

\newbox\periodbox

\def\num#1{\leavevmode\addleftdot#1\addrightdot}
\def\addleftdot{%
  \setbox\periodbox=\hbox{.}%
  \cleaders\copy\periodbox\hskip\wd\periodbox\relax
}
\def\addrightdot{%
  \setbox\periodbox=\hbox{.}%
  \cleaders\copy\periodbox\hskip\wd\periodbox\relax
}

\dorecurse{100}{The \num{2} element \num{2} xy. }

\bye

enter image description here


The order in which you combine the two skips (the \leaders and the non-\leaders one) doesn’t matter: they will always vanish as a unit.

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly 
                                 % declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\makeatletter

\newsavebox\@NWD@dot@box
\newlength\@NWD@space@skip
\newcommand*\numberwithdots[1]{%
    \unskip
    \setbox\@NWD@dot@box \hbox{.}% use current font
    \@NWD@space@skip
        \fontdimen\tw@ \font
        \@plus \fontdimen\thr@@ \font
        \@minus \fontdimen 4 \font
    \hskip \glueexpr \@NWD@space@skip-\wd\@NWD@dot@box
    \cleaders \copy\@NWD@dot@box \hskip \wd\@NWD@dot@box
    #1%
    \cleaders \copy\@NWD@dot@box \hskip \wd\@NWD@dot@box
    \hskip \glueexpr \@NWD@space@skip-\wd\@NWD@dot@box
    \ignorespaces
}

\makeatother



\begin{document}

\numberwithdots{1} note that the indent does \emph{not} count as a ``begin of
line'': not sure if this is what is wanted.  Some text \numberwithdots{2} that
includes \numberwithdots{3} some numbers: I~hope that \numberwithdots{4} some
\numberwithdots{5} of them will fall \numberwithdots{6} on a line boundary,
although \numberwithdots{7} it is \numberwithdots{8} always possible
\numberwithdots{9} to arrange things in order \numberwithdots{10} to make
\numberwithdots{11} this happen.  And it \numberwithdots{12} is also
possible\linebreak[4] \numberwithdots{13} to force \numberwithdots{14} a line
\numberwithdots{15} break\linebreak[4] at a specific \numberwithdots{16}
position.

Two numbers in a row, though, do not \numberwithdots{123} \numberwithdots{456} 
look well.

\end{document}

This is the output I get:

Output of the code

Addition

Perhaps, it would be preferable to use wider spaces around numbers with dots; and it would be even better to allow the user to customize this aspect.

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly 
                                 % declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\makeatletter

\newsavebox\@NWD@dot@box
\newlength\@NWD@space@skip
\newcommand*\@NWD@factor{1.5} % redefine default as you please
\newcommand*\numberwithdots[1]{%
    \unskip
    \setbox\@NWD@dot@box \hbox{.}% use current font
    \@NWD@space@skip
        \@NWD@factor\fontdimen\tw@ \font
        \@plus \fontdimen\thr@@ \font
        \@minus \fontdimen 4 \font
    \hskip \glueexpr \@NWD@space@skip-\wd\@NWD@dot@box
    \cleaders \copy\@NWD@dot@box \hskip \wd\@NWD@dot@box
    #1%
    \cleaders \copy\@NWD@dot@box \hskip \wd\@NWD@dot@box
    \hskip \glueexpr \@NWD@space@skip-\wd\@NWD@dot@box
    \ignorespaces
}
\newcommand*\nwdsetdotspacing[1]{\def\@NWD@factor{#1}}
\newcommand*\nwdlinebreak{\unskip\unskip\linebreak}

\makeatother



\begin{document}

\numberwithdots{1} note that the indent does \emph{not} count as a ``begin of
line'': not sure if this is what is wanted.  Some text \numberwithdots{2} that
includes \numberwithdots{3} some numbers: I~hope that \numberwithdots{4} some
\numberwithdots{5} of them will fall \numberwithdots{6} on a line boundary,
although \numberwithdots{7} it is \numberwithdots{8} always possible
\numberwithdots{9} to arrange things in order \numberwithdots{10} to make
\numberwithdots{11} this happen.  And it \numberwithdots{12} is also
possible\nwdlinebreak[4] \numberwithdots{13} to force \numberwithdots{14} a line
break \numberwithdots{15}\nwdlinebreak[4] at a specific \numberwithdots{16}
position.

Two numbers in a row, though, do not \numberwithdots{123} \numberwithdots{456} 
look well.

\nwdsetdotspacing{} % empty argument amounts to 1

\numberwithdots{1} note that the indent does \emph{not} count as a ``begin of
line'': not sure if this is what is wanted.  Some text \numberwithdots{2} that
includes \numberwithdots{3} some numbers: I~hope that \numberwithdots{4} some
\numberwithdots{5} of them will fall \numberwithdots{6} on a line boundary,
although \numberwithdots{7} it is \numberwithdots{8} always possible
\numberwithdots{9} to arrange things in order \numberwithdots{10} to make
\numberwithdots{11} this happen.  And it \numberwithdots{12} is also
possible\nwdlinebreak[4] \numberwithdots{13} to force \numberwithdots{14} a line
break \numberwithdots{15}\nwdlinebreak[4] at a specific \numberwithdots{16}
position.

\nwdsetdotspacing{2}

\numberwithdots{1} note that the indent does \emph{not} count as a ``begin of
line'': not sure if this is what is wanted.  Some text \numberwithdots{2} that
includes \numberwithdots{3} some numbers: I~hope that \numberwithdots{4} some
\numberwithdots{5} of them will fall \numberwithdots{6} on a line boundary,
although \numberwithdots{7} it is \numberwithdots{8} always possible
\numberwithdots{9} to arrange things in order \numberwithdots{10} to make
\numberwithdots{11} this happen.  And it \numberwithdots{12} is also
possible\nwdlinebreak[4] \numberwithdots{13} to force \numberwithdots{14} a line
break \numberwithdots{15}\nwdlinebreak[4] at a specific \numberwithdots{16}
position.

\end{document}

Unfortunately, for a TeXnical reason, in order to force a line break, we also had to replace the \linebreak command with our \nwdlinebreak.

Output:

Output of the second code sample

An additional degree of freedom: a factor also for the amount of backspacing. In addition to this, the following code excerpt presents an alternative, and more robust, implementation:

\makeatletter

% Alternative approach that permits nesting: use temporaries, but with grouping:
\newcommand*\@NWD@dot@factor{}
\newcommand*\@NWD@spc@factor{1.5}
\newcommand*\numberwithdots[1]{%
    \unskip
    \setbox\z@ \hbox{.}% use current font
    \dimen@ \@NWD@dot@factor\wd\z@
    \skip@
        \@NWD@spc@factor\fontdimen\tw@ \font
        \@plus \fontdimen\thr@@ \font
        \@minus \fontdimen 4 \font
    % More elegant with subroutines (or perhaps not):
    \@NWD@nonleader@hskip \@NWD@leader@hskip
    {#1}%
    \@NWD@leader@hskip \@NWD@nonleader@hskip
    \ignorespaces
}
\newcommand*\@NWD@nonleader@hskip{%
    \hskip \glueexpr \skip@-\dimen@ \relax % for robustness
}
\newcommand*\@NWD@leader@hskip{%
    \cleaders \copy\z@ \hskip \wd\z@
}
\newcommand*\nwdsetdotspacing[2][]{%
    \def\@NWD@dot@factor{#1}%
    \def\@NWD@spc@factor{#2}%
}
\newcommand*\nwdlinebreak{\unskip\unskip\linebreak}

\makeatother

Further readings

The trick of including a box in a glob of glue as \leaders, in order to have it disappear at line or page breaks, is well known: as far as I can tell, it was first proposed by Marcin Woliński in 2007, see How to make a box disappear at a line break.

See also:

  • Check if at begin of a line;

  • Is something the first item on a page?;

  • Is it possible to redefine the white space command?.

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