I think the interesting distinction is that threads, regexps, ports, etc, are communication channels, but not for higher-order values.
On May 12, 2017, 10:58 AM -0400, Scott Moore <[email protected]>, wrote: > (define (component-1 value) > (define t > (thread (lambda () > (thread-suspend t) > (for ([i (in-range value)]) > (thread-suspend t))))) > t) > > (define (component-2 thread) > (thread-resume thread) > (let* ([suspend-evt (thread-suspend-evt thread)] > [dead-evt (thread-dead-evt thread)] > [result (sync suspend-evt dead-evt)]) > (if (eq? result dead-evt) > 0 > (add1 (component-2 thread))))) > > > (define t (component-1 2)) > > (component-2 t) > 2 > > (define t (component-1 5)) > > (component-2 t) > 5 > > On May 12, 2017, 10:46 AM -0400, Robby Findler <[email protected]>, > wrote: > > I would say that the event value is the channel of communication. But, > > if this expression: > > > > (sync (thread (lambda () 3))) > > > > returned 3, then I'd say that thread itself is a channel of > > communication. But threads give themselves back to sync, not the > > values that their thunks return. > > > > Robby > > > > On Fri, May 12, 2017 at 9:41 AM, Matthias Felleisen > > <[email protected]> wrote: > > > > > > I tend to agree though there is some information flowing from a thread to > > > its context (thread CML events). I have to think whether this is a > > > channel of communication. > > > > > > > > > > > > > > > > On May 12, 2017, at 8:57 AM, Robby Findler > > > > <[email protected]> wrote: > > > > > > > > This perspective suggests a gap in the design in some sense, I would > > > > say. The PL construct cannot, on its own, guarantee that the values > > > > from #:authentic structs end up behaving like those kinds of values. > > > > > > > > (also: threads and regexps don't seem problematic from the contract > > > > perspective, but ports do, since they are a communication channel and > > > > the others aren't.) > > > > > > > > Robby > > > > > > > > > > > > On Fri, May 12, 2017 at 7:52 AM, Matthew Flatt <[email protected]> > > > > wrote: > > > > > I think a better analogy is to values like #<thread>, #<input-port>, > > > > > or > > > > > #<regexp>. Although those kinds of values are implemented with > > > > > structs, > > > > > the accessor and mutator functions are not exported (and, as Scott > > > > > says, there's no way to get the accessors and mutations by > > > > > reflection), > > > > > so there's no way to impersonate the values. In general, it's up to > > > > > the > > > > > implementation of a new kind of value to supply impersonator/chaperone > > > > > support for those values, and implementations usually don't. > > > > > > > > > > At Thu, 11 May 2017 19:00:43 -0400, Matthias Felleisen wrote: > > > > > > > > > > > > Oh right. > > > > > > > > > > > > > > > > > > > On May 11, 2017, at 6:54 PM, Robby Findler > > > > > > > <[email protected] > > > > > > wrote: > > > > > > > > > > > > > > They would be the same. We currently cannot chaperone or > > > > > > > impersonate cons > > > > > > cells. We copy them. > > > > > > > > > > > > > > Robby > > > > > > > > > > > > > > On Thu, May 11, 2017 at 5:51 PM Matthias Felleisen > > > > > > > <[email protected] > > > > > > wrote: > > > > > > > > > > > > > > Yes except that you can contract cons cells. So why couldn’t you > > > > > > > contract > > > > > > authentic structs then? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On May 11, 2017, at 6:41 PM, Robby Findler > > > > > > > > <[email protected] > > > > > > wrote: > > > > > > > > > > > > > > > > Indeed: if we did that, then these structs would be much like > > > > > > > > cons > > > > > > > > cells currently are. > > > > > > > > > > > > > > > > Robby > > > > > > > > > > > > > > > > > > > > > > > > On Thu, May 11, 2017 at 5:39 PM, Robby Findler > > > > > > > > <[email protected]> wrote: > > > > > > > > > What if #:authentic (or whatever) were only allowed on > > > > > > > > > immutable > > > > > > > > > objects and we allowed them to be copied? Then contracts > > > > > > > > > could protect > > > > > > > > > them. > > > > > > > > > > > > > > > > > > Robby > > > > > > > > > > > > > > > > > > > > > > > > > > > On Thu, May 11, 2017 at 5:38 PM, Matthias Felleisen > > > > > > > > > <[email protected]> wrote: > > > > > > > > > > > > > > > > > > > > @ Christos > > > > > > > > > > > > > > > > > > > > #:authentic explicitly introduces a channel of > > > > > > > > > > communication that it is > > > > > > not protectable by contracts. This makes Racket’s contract system > > > > > > explicitly > > > > > > incomplete. It might have been incomplete in the past for other > > > > > > reasons. > > > > > > > > > > > > > > > > > > > > If the name isn’t fixed, #:no-proxy-allowed would be my > > > > > > > > > > preference. > > > > > > > > > > > > > > > > > > > > — Matthias > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > On May 11, 2017, at 12:48 PM, Scott Moore > > > > > > > > > > > <[email protected] > > > > > > wrote: > > > > > > > > > > > > > > > > > > > > > > > I agree that generally don't want performance > > > > > > > > > > > > declarations that > > > > > > > > > > > > interfere with reasonable interposition. The good uses > > > > > > > > > > > > of `#:authentic` > > > > > > > > > > > > would be in places where the struct representation of a > > > > > > > > > > > > value is not > > > > > > > > > > > > exposed or where the values themselves are not exposed > > > > > > > > > > > > (so any > > > > > > > > > > > > interposition means being on the "inside" where you can > > > > > > > > > > > > change the > > > > > > > > > > > > code, anyway). > > > > > > > > > > > > > > > > > > > > > > Yes, I agree with this. I think as far as how this > > > > > > > > > > > changes Racket’s > > > > > > data abstraction model, the key is “where the values themselves are > > > > > > not > > > > > > exposed.” > > > > > > > > > > > #:authentic only has an interesting effect in the other > > > > > > > > > > > case, where > > > > > > “outside” code gets its hands on a value of the struct type. > > > > > > Previously, I > > > > > > could write a program that used inspectors to impersonate this value > > > > > > regardless of the “inside” code’s intent. Now that would no longer > > > > > > be possible. > > > > > > > > > > > > > > > > > > > > > > I doubt there is much code that currently relies on being > > > > > > > > > > > able to do > > > > > > this and so I would say go ahead. (Perhaps DrRacket or other > > > > > > debugging tools?) > > > > > > > > > > > > > > > > > > > > > > On the other hand, Spencer already asked if this would be > > > > > > > > > > > something the > > > > > > optimization coach would recommend. I think it would be important > > > > > > for the > > > > > > documentation of #:authentic or the implementation of such a coach > > > > > > to stress > > > > > > the importance of the rules of thumb you just laid out. > > > > > > > > > > > > > > > > > > > > > > -- > > > > > > > > > > > You received this message because you are subscribed to > > > > > > > > > > > the Google > > > > > > Groups "Racket Developers" group. > > > > > > > > > > > To unsubscribe from this group and stop receiving emails > > > > > > > > > > > from it, send > > > > > > an email to [email protected]. > > > > > > > > > > > To post to this group, send email to > > > > > > > > > > > [email protected]. > > > > > > > > > > > To view this discussion on the web visit > > > > > > https://groups.google.com/d/msgid/racket-dev/3c430798-e93a-4900-8215-198f77d9b9 > > > > > > 91%40Spark. > > > > > > > > > > > For more options, visit > > > > > > > > > > > https://groups.google.com/d/optout. > > > > > > > > > > > > > > > > > > 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