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!
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