@peeja it's so you can provide additional options to map.

Oh, I see. That makes sense.

@val_waeselynck take a look at this code: https://github.com/clojure/core.async/blob/master/src/test/clojure/clojure/core/async/ioc_macros_test.clj

@val_waeselynck the idea is that you can provide custom hooks to the macro that tell it when to pause the machine and hand control over to a function that decides what to do next. It's not a public api so it may change in the future, but it hasn't changed in about 3-4 years, so take the risk if you want 🙂