Re: Marginal line numbers

["Thomas A. Schmitz" <thomas.schmitz@uni-bonn.de>]

On Dec 16, 2010, at 10:28 PM, Jon Crump wrote:

> Thomas, et alia.
> 
> Thanks so very much! I now have this:
> 
> \startluacode
> function filter(s)
>   if math.mod(s,5) == 0 then
>     context.color( { "darkred" }, s )
>   end
> end
> \stopluacode
> 
> \define[1]\MyNumber%
> {\ctxlua{filter(#1)}\endgraf}
> 
> \startxmlsetups xml:lb
> 	\lineNumbers{\MyNumber{\xmlatt{#1}{n}}}
> 	\xmlflush{#1}
> \stopxmlsetups
> 
> \defineinmargin [lineNumbers] [outer] [normal]
> 

This was just an example to show you how to use lua to do things which are difficult or impossible or cumbersome in TeX alone, such as math, working with strings (substitutions, etc.), conditionals, loops... You don't have to take my code verbatim; the "darkred" was just meant to show that you can apply certain code to a number if it matches a condition (here: be divisible by 5).

> This gets me what I wanted.  Still fumbling greatly with the macro
> syntax. I'm not sure what the recursion is for, for example. On the
> other hand the lua seems rather straightforward to me by comparison. I
> tried returning an empty string like this: context.color( {"blue"}, ''
> ) to remove the other numbers, but that seemed silly, so I just
> removed the 'else' clause instead, and that seemed to work as well.
> 

Yes, of course, if all you want  is process numbers divisible by 5, that's the easiest way. But it's good to know that lua allows more complex conditionals - you could use "elseif"s to make numbers divisible by 100 bold, or whatever. I find such conditionals in TeX much more cumbersome; even for somebody with no programming background like myself, they are easy to write in lua.

The recursion was just a way of demonstrating the effect. \dorecurse is a wonderful macro to construct minimal examples (you can search the mail archive for some real gems). And, as a hint: constructing a compilable minimal example not only is educational (I don't know how often I could solve my problems when I tried to produce a minimal example and saw where my approach was failing), but will also improve your chances of people actually willing to help you. If you want to see an elegant way of producing minimal examples in xml, search the mail archive for "xmlprocessbuffer."

Thomas
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