[damart]

Futures/promises seem like they're basically just a limited subset of FRP (Rx, RAC) observables/streams - such that they either "next" once and "complete", or "error" without "nexting".

I suppose they also have caching built in, but that is easy to build on top of FRP.

[learc83]

Yeah, I think you're right on the money. Matt Podwysocki has a chart explaining how promises fit in to all of this but I can't seem to find it. Here's what he says in the RxJs documentation.

"One question you may ask yourself, is why RxJS? What about Promises? Promises are good for solving asynchronous operations such as querying a service with an XMLHttpRequest, where the expected behavior is one value and then completion. The Reactive Extensions for JavaScript unifies both the world of Promises, callbacks as well as evented data such as DOM Input, Web Workers, Web Sockets. Once we have unified these concepts, this enables rich composition."

[fugalh]

Indeed, any good intro to Rx points this out: Observable is the plural of future/promise.

When people are trying to do fancy streaming stuff with futures and come to me for help, I generally recommend they do the streaming with Rx instead. (eg rxcpp from Microsoft)