You have a pretty narrow definition of a platform. Consider https://en.m.wikipedia.org/wiki/Computing_platform https://en.m.wikipedia.org/wiki/Computing_platfor

You have a pretty narrow definition of a platform. Consider https://en.m.wikipedia.org/wiki/Computing_platform https://en.m.wikipedia.org/wiki/Computing_platform Yes, you are right, I didn't consider the checkcast instruction. Yes, F# does not have this particular limitation, but has few of its own in different places. Most notably, it lacks HKT (arguably, because of CLR awareness of generics). BTW, alternative approaches to stack-safe recursion do exist in Scala. For example, https://github.com/slamdata/matryoshka https://github.com/slamdata/matryoshka