Re: how to extend a capability on a data source?

Thanks for the correction and clarification.

On Mon, Nov 4, 2013 at 8:30 PM, Kevin Reid <kpreid-M/[email protected]> wrote:

> On Nov 3, 2013, at 21:44, David Barbour <[email protected]> wrote:
> > On Sun, Nov 3, 2013 at 9:06 PM, Rob Withers <[email protected]> wrote:
> >>> Those properties together would make the Resolver linear, and would
> ensure that the promise is fulfilled once and only once (modulo divergence
> of the resolver computation).
> >> To my recollection, this is precisely what Elib delivers.
> > When I say "ensure", I think I'm saying something stronger than you're
> hearing. Elib does not make a *static guarantee* that a resolver is called
> exactly once. If a programmer simply drops the resolver, it is never
> called, and thus Elib needs a concept of "broken" promises.
>
> I'm not following the conversation, so this is strictly a technical
> nitpick about E:
>
> A broken promise is not one which has never been resolved, but one which
> has been resolved to a failure. (More precisely, a promise is resolved to
> another ref, which happens to be a broken ref.) A promise whose resolver is
> never used simply remains unresolved forever.
>
> If the state of a promise revealed that its resolver has been dropped,
> then that would expose GC nondeterminism even in the single-vat case, so we
> don't do that.
>
> --
> Kevin Reid                                  <http://switchb.org/kpreid/>
>
>
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