[luatex] How to define an internal register?

Henri Menke henrimenke at gmail.com
Sat Jan 26 06:58:34 CET 2019

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


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.


local value = 0
function register()
    local str = token.scan_string()
    if str then
        local int = string.gsub(str,"=","")
        value = tonumber(int)
        tex.sprint([[\numexpr]] .. value .. [[\relax]])





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