Well, it's not restricted to pointers - In general I would think that the type annotation for Some | None would be left alone. I just used pointer as an example because pointers exclude a value, 0x0, from the valid set. In which case None is encoded as 0x0.

Thanks for the bit about polymorphism in the context of what a compiler would see - clients that do not see the hypothetical additional annotation for that specific type to allow a format wouldn't have the augmented operational needs to work on such an instance correctly. Got it!

On Tue, Aug 18, 2015 at 2:57 PM, Hendrik Boom <hendrik@topoi.pooq.com> wrote:

On Tue, Aug 18, 2015 at 01:06:55PM -0400, Kenneth Adam Miller wrote:
> I was wondering if cases where format control is possible in typing
> constructs can allow things like restricting the implementation size after
> compilation of a specific variant type. Say, for instance that I wanted to
> have a malloc implementation instead of returning a Some 'a | None type
> that compiles down to a boxed case of first a word and then the subsequent
> 'a instance, down to the 'a instance, where in the values of the word enum
> (or tag) are not present in the possibilities of the 'a instance.
>
> Maybe it sounds silly, but in really tight loops you want to squeeze for
> efficiency. So I was wondering if maybe the same actual code be used with
> the same sanity of type checking, but some annotation provided at the type
> declaration to allow such optimization to take place.

Let's see. OCaml steals a bit to indicate whether a valus is a pointer
or not, right? Could that bit see duual usage for the option type? So
that if it's an optional pointer type, the bit is left off, and if it's
an optional nonpointer type, it's turned on (and set to point to
location zero, which the GC couls check for)?

THe proble I see with this is if the 'a is passed to a generic function
where iti isn't statically known where it's a pinter or not. The
conpiler will not know whether to test for absence or presence of the
bit.

-- hendrik