[racket] [racket-dev] Implementing contracts for async channels

I’ve written up the relevant documentation, so I think this is more or less complete. I’ve submitted a pull request here <https://github.com/plt/racket/pull/860>. I went ahead with my gut instincts and put the documentation with the racket/async-channel documentation rather than the contract and impersonator documentation, since I think it makes more sense there.

The only remaining potential problem is the impersonate-evt issue outlined previously. Frankly, I’m not even sure how to test that, much less work around it, so if it’s a real issue, I’d probably need some advice in fixing it. (I’m not even really sure how to devise a contract that would produce an impersonator contract.)

I’ve also implemented the accompanying changes in Typed Racket and submitted a pull request here <https://github.com/racket/typed-racket/pull/12>. Obviously, since that depends on the Racket changes, it can’t be pulled until the changes are merged, but I figured I’d submit a pull request anyway in case there are any changes that I need to make to the Typed Racket implementation.

> On Jan 15, 2015, at 23:07, Alexis King <lexi.lambda at gmail.com> wrote:
> 
> 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 <mailto: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 <mailto: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 <mailto: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 <mailto: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 <mailto: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 <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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