[luatex] How to define an internal register?

[David Carlisle]

Wouldn't it be easiest just to define it with \newskip to get the tex
input syntax and then access that skip register from lua?

David

On Sat, 26 Jan 2019 at 05:59, Henri Menke <henrimenke at gmail.com> wrote:
>
> Dear list,
>
> I am trying to define a command which behaves like an internal register
> using the `token` library.  However, there are some complications.  For
> example a register has to be settable using both
>
>    \register=<number>
>    \register<number>
>
> Additionally, if no number is given it should raise a “cannot be used in
> vmode” error or similar.  Also it has to be possible to get the value
> using `\the`.  Below you can find a minimal example where I have already
> achieved some of these things but others fail miserably.
>
> Cheers, Henri
>
> P.S.: I have also attached a much more complex example, so you can see
> that I actually want to emulate pdfTeX's \pdfadjustinterwordglue.
>
> ---
>
> \directlua{
> local value = 0
> %
> function register()
>     local str = token.scan_string()
>     %
>     if str then
>         local int = string.gsub(str,"=","")
>         value = tonumber(int)
>     else
>         tex.sprint([[\numexpr]] .. value .. [[\relax]])
>     end
> end
> }
>
> \protected\def\register{\directlua{register()}}
>
> \register=1
> \register=12
> \register=123
>
> \register1
> \register12
> \register123
>
> \the\register
> \the\register
> \the\register
>
> \bye