At Thu, 30 Aug 2012 09:34:09 -0400, Asumu Takikawa wrote: > On 2012-08-30 06:53:58 -0600, Matthew Flatt wrote: > > That variant is called `call/cc-via-composable' in the tests. It's > > meant for use with `call-with-continuation-prompt-for-composable', > > which is why there is an extra `call-with-continuation-prompt'. > > I think you may want the extra prompt in there, because a `call/cc` > currently does not drop the prompt when it installs the new > continuation. On the other hand, after the abort handler is run, the > prompt is discarded.
The default abort handler keeps the prompt (i.e., it installs a prompt with the same tag as the abort target) when it runs a thunk that is supplied to the abort. > The example that would break uses `call/cc` and delimiters to implement > `amb`. [...] > The abort handler here isn't prepared to deal with thunks that it would > receive from an emulated `call/cc`. Ok, it makes sense that we'd have to break that example. > > 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. > > Did you mean behaves like the replacement if there *is* an intervening > prompt? Sorry --- I meant "if there is no shared `dynamic-wind' before the prompt". _________________________ Racket Developers list: http://lists.racket-lang.org/dev
