LUA - 如何使用_G [x]（）方法从字符串中调用函数

Question

I'm having a problem with my code and I don't know what's up, I've searched online and the _Gx method was suggested as the best way over ones like loadstring(x)... although I would be happy with either, can't get either one to work. What I want to do is, in ComputerCraft, send a function name and argument to a turtle, which I'm doing by saving both values to a table and sending across the table, and then on the turtle's program, have a big list of functions, and using a command, call them from the string sent and insert the arg as well. My error is "attempt to call nil", which I don't quite understand why it's saying that... Thanks in Advance!

EDIT

I've edited my code down, as asked, to show that even stripping all else away, this still fails. I could even strip it down even more by taking the variable completely out, and putting the string straight into the _G. This still fails even doing it like that. I've decided to keep it in because that's how I am actually going to be using it later. Calling the function normally works fine. I'm using version Luaj-jse 2.0.3

function foo ()
  print ("HI!")
end

print (_VERSION)

Answer 1

I don't know what rednet is, but it seems like you passes name of function to another Lua VM, which doesn't know anything about this function (this function is absent in that VM's globals table).
So, passing function definition as string and executing it by receiver with loadstring is the only solution.