Experiment: adding an [nb_occurs] function.

[rlepigre]

This is one possible way to address #29, but it is not clear this is what we want since it might impact performance. In particular, we introduce an extra pointer indirection since we cannot unbox the anyvar type anymore.

[craff]

If also does count very well in all cases: if you define

let self_app : term box -> term box =
  fun t -> box_apply (fun t -> App(t,t)) t

If will count variable in t only once. It is not clear what the user wants in such a case.

[rlepigre]

That's a good point, I guess this approach can only work if the argument of functions passed to box_apply and friends is always used linearly (which I think is pretty much always the case (?)).

In any case, this PR is really just an experiment, it is really not clear to me whether we want/need this.

[craff]

I can review the PR ... or we drop it ?

[rlepigre]

We should probably drop it at this point, given the problem you highlighted.