Implement completion/exception handling callbacks for promises and futures

Question

Based on https://dev.clojure.org/display/design/Promises

Discussion on Slack:

Enhance future/promise to be able to call a function on completion/failure (I'd use promises a lot more if I had this functionality but you can sort of hack around it in ugly ways with futures and/or additional functions/macros).

Answer 1

Reference: https://clojure.atlassian.net/browse/CLJ-2487 (reported by seancorfield)

Answer 2

The design document moved to https://archive.clojure.org/design-wiki/display/design/Promises.html and it predates java.util.concurrent.CompletableFuture which provides all of those features (and more).

After some discussion with Ghadi, I decided to just write a few macros to provide syntactic sugar for the basic operations I needed. They can be found in https://github.com/worldsingles/commons

(-> (completable (do-some-stuff))
    (then some-function)
    (exceptionally an-exception-handler)
    (deref))