const char* sglua_tostring(lua_State* L, int index);
const char* sglua_keyvalue_tostring(lua_State* L, int key_index, int value_index);
const char* sglua_tostring(lua_State* L, int index);
const char* sglua_keyvalue_tostring(lua_State* L, int key_index, int value_index);