The three event bits in a pointer could be used as tags if the GC isn’t using them for garbage collection support. Mill pointers are always 64 bits. If is made enough of a difference I suppose we could be talked into one more bit 🙂
It would be possible to add a few metadata bits, or steal the floating-point metadata bits, for use as tags. However, the tags would be lost when the pointers are stored to memory, because memory has no metadata. Any ideas on what might be done about that?