[texhax] Question about math fonts in LaTeX

[Philipp Stephani]

>
>Von: Vafa Khalighi <vafakhlgh at gmail.com>
>An: texhax at tug.org
>Gesendet: Donnerstag, den 20. Januar 2011, 14:41:15 Uhr
>Betreff: [texhax] Question about math fonts in LaTeX
>
>
>Can you change the font of \mathbf so that the font of only digits  changes and 

>everything else will be typeset in the default font. For  example, say your 
>default font for \mathbf is cmr but you only want to  change the font of digits 

>inside \mathbf to cmtt and nothing else so  that $\mathbf{xyz0123}$ give you xyz 
>
>in cmr but 0123 in cmtt. Is  this doable? (of course without creating a new font 
>
>or modifying an existing font)

Here is a hackish solution:

\documentclass{minimal}
\usepackage{xparse}
\DeclareSymbolFont{monospace}{OT1}{cmtt}{m}{n}
\ExplSyntaxOn
\cs_new_eq:NN \orig_mathbf:n \mathbf
\RenewDocumentCommand \mathbf { m } {
  \orig_mathbf:n {
    \prg_stepwise_inline:nnnn { `0 } { \c_one } { `9 } {
      \mathcode ##1 = \numexpr "100 * \symmonospace + ##1 \relax
    }
    #1
  }
}
\ExplSyntaxOff
\begin{document}
$abc 012 \mathbf{abc 012} abc 012$
\end{document}