The backward compatibility issue Mike is ranting about in this post is not in the language, it is in the source code of Lua itself (actually a define in its con

The backward compatibility issue Mike is ranting about in this post is not in the language, it is in the source code of Lua itself (actually a define in its configuration header file). There was a very good reason for this change, which is that Lua introduced an integer type instead of using floating point numbers for everything. This means that LUA_NUMBER_DOUBLE and LUA_NUMBER_FLOAT do not really make sense anymore (when you check those you may want to check the type of the integer numbers or the type of the floating-point numbers). In any case, porting luabitop doesn't really matter that much: if LuaJIT supported Lua 5.3 people would use the native 64 bit bitwise operators it introduced instead.