I'd be very interested in a low level FP without GC (including reference counting), as well. I believe a major difficulty is how do deal with closures. Obviou

I'd be very interested in a low level FP without GC (including reference counting), as well. I believe a major difficulty is how do deal with closures. Obvious solutions include region inference and copying the closure, both with obvious downsides. Another difficultly is how to deal with structure sharing, a technique required for the efficiency of almost all functional data structures.