[racket-dev] Implementing contracts for async channels

From: Alexis King (lexi.lambda at gmail.com)
Date: Fri Jan 16 02:07:25 EST 2015

Sure thing, done. I’ve moved everything into racket/async-channel, added the missing functions, and added some tests. I squashed my commits into one, and the result is here:
https://github.com/lexi-lambda/racket/commit/0074ba13b712a87c9d05948ae075bcd74c7651e7 <https://github.com/lexi-lambda/racket/commit/0074ba13b712a87c9d05948ae075bcd74c7651e7>

Two simple points remain:

Where should the documentation go? Should it be under contracts or async-channels? I’d prefer the latter, but I’m not sure.
Since there is no impersonate-evt function, I don’t think my impersonate-async-channel function will actually work. Is that an accurate concern? How could I fix it?

Otherwise, I think this works fine and is probably ready to go.

> On Jan 15, 2015, at 15:09, Robby Findler <robby at eecs.northwestern.edu> wrote:
> I think they should probably all be exported from racket/async-channel.
> Unless there is some reason to modify the internals of racket/contract
> to support them?
> Robby
> On Thu, Jan 15, 2015 at 4:50 PM, Alexis King <lexi.lambda at gmail.com> wrote:
>> Sorry, I wasn’t clear. The chaperone/impersonate-async-channel functions are exported from racket/async-channel. The async-channel contracts, however, are exported from racket/contract.
>>> On Jan 15, 2015, at 14:41, Robby Findler <robby at eecs.northwestern.edu> wrote:
>>> Just a small nit: why export that function from racket/contract and
>>> not an async-channel library?
>>> Robby
>>> On Thu, Jan 15, 2015 at 3:33 PM, Alexis King <lexi.lambda at gmail.com> wrote:
>>>> As an update, I’ve made a bit more progress on this. I’ve implemented an
>>>> impersonate-async-channel function, and I’ve actually included this in the
>>>> exports from racket/contract. I also realized the blame information is
>>>> correct, it works fine. Most of the other issues remain, as well as a few
>>>> new questions:
>>>> There is no impersonate-evt function, so I’m not sure that my implementation
>>>> will work. What should I do about this?
>>>> I’d assume this needs to be documented/tested as well. Where should those
>>>> things be located?
>>>> On Jan 14, 2015, at 23:44, Alexis King <lexi.lambda at gmail.com> wrote:
>>>> Currently, async channels do not have contracts to check their contents.
>>>> This is a problem for Typed Racket, and it prevents typed code from
>>>> interacting with code that produces async channels.
>>>> I started looking into how to add contracts to the language, and it seems to
>>>> use the chaperones/impersonator system, as I suspected. However, async
>>>> channels obviously cannot be impersonated, so I needed to implement that as
>>>> well.
>>>> I modified the async-channel struct to use generics to allow it to be
>>>> impersonated or chaperoned, which I have exposed by implementing
>>>> chaperone-async-channel. I then tried implementing async-channel/c. The
>>>> internals of the contract system are a little beyond me, but I got a working
>>>> solution by following the example of the box contracts.
>>>> My work thus far can be found here:
>>>> https://github.com/lexi-lambda/racket/commit/84b9f3604891f3f2061fb28ed4800af8afa4751b
>>>> First of all, is this a correct approach? Have I done anything wrong, or
>>>> should I have done anything differently? I didn’t find much documentation on
>>>> the internals of either of these systems, so I mostly went about things as I
>>>> found them.
>>>> Second, obviously, not everything is implemented here. Among the additional
>>>> necessary changes are:
>>>> I need to implement support for impersonators and impersonator contracts
>>>> (right now I’ve only bothered to do chaperones).
>>>> I need to implement async-channel/c-first-order and
>>>> async-channel/c-stronger. I can probably figure out the latter, but I’m not
>>>> even sure what the former is supposed to do.
>>>> I need to implement a wrap-async-channel/c macro for the export. I’m not
>>>> sure how this works, either. From looking at wrap-box/c, it seems to add
>>>> some syntax properties, but I’m not sure what they do or how they work.
>>>> Somehow, the blame information has to be correct. Is that what the wrap
>>>> function does? Or do the async-channel functions need to be updated to
>>>> assign blame?
>>>> I’d really like to get this working, and I think I’m close, but I’m a little
>>>> inexperienced. I’d appreciate any help, even if it’s just pointing me in the
>>>> right direction.
>>>> Thanks!
>>>> _________________________
>>>> Racket Developers list:
>>>> http://lists.racket-lang.org/dev

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