Re: [Caml-list] Type Encoding Format Control

[Kenneth Adam Miller <kennethadammiller@gmail.com>]

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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
>

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