Maybe the "elegance" is a factor as well, but I haven't seen it mentioned. All I've seen mentioned is: a) can't change syntax b) can't take huge performance hit

Maybe the "elegance" is a factor as well, but I haven't seen it mentioned. All I've seen mentioned is: a) can't change syntax b) can't take huge performance hits at run time or at compile time c) can't break backwards compatibility d) talk is cheap - provide a working implementation So far, nobody has been able to show all 4 of these requirements, so nothing has been done. But when/if someone does, I expect it to be taken very seriously.