The important bit seems to be the behavior of the _Bool type, not the macroness (also, the [Future Directions section of the Open Group spec](http://pubs.opengr

The important bit seems to be the behavior of the _Bool type, not the macroness (also, the [Future Directions section of the Open Group spec](http://pubs.opengroup.org/onlinepubs/007904875/basedefs/stdbool.h.html#tag_13_46_06 http://pubs.opengroup.org/onlinepubs/007904875/basedefs/stdb...) says #undefing and redefining the macros is obsolescent, leaving open the possibility of changing the implementation from a macro to something else entirely).