Clojure Q&A - Recent questions tagged flow

Typos in Flow guide

Mon, 18 Aug 2025 08:19:35 +0000

As reported by a Hacker News user, there are typos in the Flow Guide :

"excepiton" should be "exception"
"provded" should be "provided"

and also, it seems that in the transition section, "The description arity takes the current state ..." should be "The transition arity takes the current state ..."

Is core.async.flow available in ClojureScript?

Thu, 17 Jul 2025 08:31:10 +0000

Hi,

I know it's early days for core.async.flow but I thought I would give it a try in one of my ClojureScript projects.

I've got {:mvn/version "1.9.808-alpha1"} in my deps.edn but I'm getting the following error when I try to access the namespace:

No such namespace: clojure.core.async.flow, could not locate clojure/core/async/flow.cljs

Thanks for your help.

How best to call long-running tasks from a core.async.flow process?

Wed, 09 Jul 2025 18:31:41 +0000

I'd like to write to a database as the final process in a core.async.flow flow. The db load can take several minutes. If I do this work directly in the :transform function's thread, flow-monitor can't ping that process for the duration of the load. But if I offload the work to a different thread and return from the :transform function, I can't as easily control back pressure from that process.

The relevant process currently looks something like:

(def db-loader
  (flow/map->step
   {:describe (fn [] {:workload :io
                      :ins {:in "Batched items"}})
    :init     (fn [state] state)
    :transition (fn [state status] state)
    :transform (fn [state _ batch]
                 (t/log! "DB Loader is loading a batch.")
                 (Thread/sleep 10000) ;; imagine this code writes to the db.
                 (t/log! "DB Loader loaded a batch.")
                 [state])}))

A more complete code example is at https://gist.github.com/tomconnors/245fb69ed757b34502c8d57637db8de2.

Is there a better option for this process?

what kind of systems could be made with clojure.async.flow?

Tue, 29 Apr 2025 15:48:35 +0000

Trying to capture mechanical essence of clojure.async.flow with basic terms instead of flow own terms i guess that clojure.async.flow allows to structure a system as a set of stateful functions running concurrently in the same jvm process and interacting with each other explicitly via channels.

what kind of systems could be made with clojure.async.flow?

it's definitely not naive service which handles API http requests, transforms it somehow and puts it into database.