[texhax] dual-use input/output macro

[Philip G. Ratcliffe]

> Suppose I want to show both the TeX input and its corresponding output
> as an example.  Not big files, but just small fragments.  As in:
> 
>   \showme{hello, \relax there}
> 
> and the typeset output could be, say, two lines:
> 
>   hello, \relax there   % in typewriter
>   hello, there          % in roman
>   
> I cannot think of any easy way to do this.  About all I can imagine is
> changing all the catcodes to other before reading the argument, printing
> the arg in tt, then writing the arg to an external file, and 
> reading it back with normal catcodes to get the normal output.
> 
> Is there a simpler way?  Has anyone programmed the above?  I imagine
> e-tex's \scantokens and \readfile (or something else?) might be useful,
> but didn't see a quick application.
> 
> I browsed through the fancyvrb, verbatim, etc., doc but nothing jumped
> out at me.

How about something along these lines?

\documentclass{article}
\usepackage{fancyvrb}
\begin{document}
\DefineShortVerb{\|}
\def\showme|#1|{\SaveVerb[aftersave={\UseVerb{showme} = #1}]{showme}|#1}
\showme|hello, \relax there||
\end{document}

Cheers,  Phil Ratcliffe