Compare to coro package

[king-of-poppk]

There is a package on CRAN named coro that seems to implement essentially the same primitives on top of the promises package. What are the differences between that package and the async package?

[crowding]

1. async objects print a bit more state information (showing you where they are paused)

2. async::gen generators are cross compatible with the older R iterators protocol (as used by e.g. the foreach package), and companion package iterors includes a lot of tools to work with them.

3. the await() method includes an error argument, which allows you to handle promise errors with less boilerplate than using tryCatch.

4. channels/streams (asynchronous iterators.) Currently I'm working on expanding channels to work with non-blocking connection objects, which will be nice for networking and parallel computing applications.

5. While not yet completed, the 1.0 release of async will include a compiler, that should improve performance by >10x at least.

[king-of-poppk]

Cool! What about interoperability with the future and promises packages?

PS: OK, sorry, interoperability is there, just had to read the README.

[king-of-poppk]

Another related question: does async suffer the same issue as r-lib/coro#39 ?

[crowding]

async() constructs a promise object, and the argument to await can be anything for which an as.promise method is defined, including Future.

The other question is touched on in the language vignette.
async and stream objects always wind on a top-level tryCatch, so any errors during execution should result in promise rejections.
(Generator objects on the other hand will let errors raise to the caller of nextElem).

> f <- async(function() {stop("oops!")})
pr <- f(); pr |> then(\() print("resolved!"), \() print("rejected"))
Warning message:
In cps_translate(expr_, async_endpoints, split_pipes = split_pipes) :
  no keywords (break, next, return, for, switch, goto, on.exit, await, awaitNext) used?
> [1] "rejected"
> pr
async({
    stop("oops!")
})
<environment: R_EmptyEnv>
<async [rejected at `pump__doExits`: <simpleError in eval(val, targetEnv): oops!>]>
<Promise [rejected: simpleError]>

(The warning message is complaining that async(stop()) is kind of pointless because it doesn't have any await calls.)