skaller writes:
 > > > Boxed values can use a null pointer for none.
 > > 
 > > I have a question--how is this different (except for the efficiency of
 > > using null) from using a 'a option array?
 > 
 > 	It isn't, in theory, it is exactly the same (and therefore sound).

I think (correct me if I'm wrong, sorry) that this is a return to an
issue which seems to be a bit of an FAQ.

The problem is that if you have a value of the type `int option
option', you have to be able to distinguish between `None' and `Some
None'!  If both the enumeration-indirections are elided, you can't; if
only one of them is, you have inconsistency which would presumably
have to be resolved using whole-program optimisation or something.

For the lowdown and an interesting proposal for a fix, see

	http://caml.inria.fr/caml-list/0967.html

The same idea would obviously apply to arrays.