Thank you @TinBryn, that is along the lines I was looking for. Just to note
that the only cast required is in the `update` method above. All the other
calls to `StateFn( .. )` can be omitted, i.e.
return lo
Run
works the same as
return StateFn(lo)
Run
I had expected the compiler to complain about the casting, but even with all
the `{.gcsafe.}` directives there are no warnings.
