Get value of macro from lualatex directly

Question

I need to get the value of a macro from lualatex directly and return it in a function call

function GetMacroValue(macro)
    return macro.value
end

I've tried various things such as using tex.print to store the value in a temp value BUT since tex.print executes after the function call/luacode block it does not work

function GetMacroValue()
    tex.print("\\directlua{value = tonumber('\\the\\"..macro.."')}")
    return value
end

Would work except the tex.print line does not execute until after the fact in which case the previous value is returned.

since tex.execute does not exist yet is there any other method? I've tried coroutines but it does not work for(or I can't get it to work).

Answer 1

If it's a count register, you can access it directly (tex.count[...]). Similar for other stored items such as toks, skip, dimen and attribute registers. See manual section 4.13.4.

If it is something you only get "during runtime" you have to use coroutines for that. I have written an answer to another question where I have given a short working example for a coroutine:

https://tex.stackexchange.com/a/20905/243

Answer 2

It seems the only way to get some of these tex values is by passing them to lua. This maybe due to bugs in lualatex as the manual states it is possible. The problem exists because there is no way for lua code to pass control back to TeX(to get the variable) and then continue where it left off. Coroutines should allow this behavior but throw an exception due, at least in my case, to some mismatch between TeX and Lua.

The best way I've come up to solve this problem is to write a macro that passes all the variables from TeX to Lua I need and have it called transparently each time lua code is executed(by wrapping \directlua).