[Dev-luatex] register a callback on macro expansion?

Hi, I'm wondering if I can register a Lua function as callback on the expansion of a specific macro? I'm expecting something like this: \def\hello#1{#1} callback.register("macro.hello",lua_func_hello) when using \hello{abc}, the lua_func_hello will get called and have access to the arguments of \hello (abc). In this way, we can implement loop structure in lua (which I think is a cleaner way than tail recursion in TeX). - jjgod.