The third has to do with how local variables are managed for functions defined at runtime - while you could rewrite code with macros to pass an implicit closure value array to the function at all points of use, it would be quite a bit less awkward to have it part of the language proper. Heck, it's not that unusual to have C functions that take a void * argument for "userdata"; the function/userdata combination is one way of representing closures when compiling to C.