At Thu, 30 Aug 2012 11:36:55 -0400, Asumu Takikawa wrote: > On 2012-08-30 06:53:58 -0600, Matthew Flatt wrote: > > I think this combination of replacing both `call/cc' and `dynamic-wind' > > would be equivalent to a smaller change to the semantics of `call/cc', > > which is that it behaves as it does now if there's a shared > > `dynamic-wind' between the source and target continuations, but it > > behaves like your replacement `call/cc' if there's no intervening > > prompt (which addresses the reasoning problem). Also, implementing the > > change directly in the existing `call/cc' implementation sounds fairly > > easy to me. > > Sam and I discussed this some more, and we think it sounds workable and > will go and try to add it to the Redex model and see what tests fail. We > were concerned about one thing though: it sounds like this would modify > the behavior of `call/cc` depending on whether or not you put a > `dynamic-wind` in your continuation. > > That also means that a programmer who installs a `dynamic-wind` might > get fewer abort handlers run than expected, or perhaps gets *more* run > than expected since they either didn't install the `dynamic-wind` or > they passed the continuation out of the `dynamic-wind` to a different > context and invoked it there. > > Is that a fair point or are we misunderstanding your proposed semantics?
Yes, that's true. I don't think there will be a difference for typical uses of `call/cc' and typical abort handlers, though. And as I understand it, we're not at this point trying to make `call/cc' work seamlessly, but instead support it reasonably well for backward compatibility. _________________________ Racket Developers list: http://lists.racket-lang.org/dev
