Another advantage of #define PRIMITIVE - it doesn't steal a handy 1-char identifier that the consuming program might want to use for its own purposes. And as we

Another advantage of #define PRIMITIVE - it doesn't steal a handy 1-char identifier that the consuming program might want to use for its own purposes. And as well as making a longer identifier, I'd also personally suggest also adding a library-specific prefix, to further reduce the risk of conflicts. (I have worked on code where the debug print macro was called P...)