Question: Wrap an async operation (e.g. java.util.Future) inside of an Either?

[SkylerLutz]

Is it possible to convert an async operation (e.g. fetch records from a database and wrap in a future) to an Either or a Maybe?
If not, is it on the roadmap? Why or why not?
I discovered IO.externallyManaged() but it requires me to invoke Future.get() on my future. I am looking for a way to use the palatable/lambda API exclusively to invoke my async calls.

Thanks

[jnape]

Hi Skyler,

Are you talking about something like this?

Either<Throwable, A> either = Try.trying(myFuture::get).toEither(); // or .toMaybe()

If so, in general I would avoid that, since the Future almost certainly represents a side-effect, and I tend to keep impure operations separate from pure operations. In this case, I would lift the Future into an IO:

IO<Either<Throwable, A>> io = io(myFuture::get).safe(); // or .fmap(Either::toMaybe)

Now, this is about the best you can do if all you have is a Future. Future is a miserable type precisely because it offers no interface for composition or callbacks, which severely limits what can be done with it that doesn't require a call to Future#get.

However, if you had a CompletableFuture, I can lift that into an IO directly via the mechanism that you've already discovered, IO#externallyManaged.

Once you're in IO, you should have no trouble at all wrapping the result in an Either, or a Maybe, or whatever you choose.

So, is the challenge that you just have a Future, and not a CompletableFuture, and you also don't want to call Future#get? If so, I have personally gone to great lengths in the past to proxy Future with CompletableFuture at the expense of a single JVM thread acting as an event loop or selector (think of it as epoll for futures) that connects CompletableFutures to their proxied Future, and I can explain how that worked if you're interested, but that code is not in lambda, and I probably wouldn't put it in lambda since it would require lambda taking one of your threads away from you at start up time.

[jnape]

If you'd like to discuss this in real time, if that's easier, please join me in the lambda gitter and we can chat about this: https://gitter.im/palatable/lambda

[jnape]

Continuing this conversation on the gitter channel, so closing.