help with callbacks

[Merick <Merick_TeVaran@...>]

I'm using FreeBasic to make a script interpreter and have started adding 
wrappers for a gui library. Some of the functions for the gui take a 
pointer to a user-created function as one of the arguments. Can anyone 
tell me how to do this with functions created inside the lua script? I 
know it probably has something to do with lua_ref() but I just can't 
figure it out.