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core.async debounce
(defn debounce [in ms]
(let [out (chan)]
(go-loop [last-val nil]
(let [val (if (nil? last-val) (<! in) last-val)
timer (timeout ms)
[new-val ch] (alts! [in timer])]
(condp = ch
timer (do (>! out val) (recur nil))
in (recur new-val))))
out))
@felixflores

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felixflores commented Dec 8, 2014

Thanks for this 😃

@aiba

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aiba commented Apr 18, 2016

Nice!

@wilkerlucio

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wilkerlucio commented Jun 20, 2016

nice, just one comment, this implementation has one issue, that is when you close the in channel it gets into an infinite loop by recurring with new-val as nil all the time, the fix is simple, just check the value when receiving from in:

(defn debounce [in ms]
  (let [out (chan)]
    (go-loop [last-val nil]
      (let [val (if (nil? last-val) (<! in) last-val)
            timer (timeout ms)
            [new-val ch] (alts! [in timer])]
        (condp = ch
          timer (do (>! out val) (recur nil))
          in (if new-val (recur new-val)))))
    out))
@danieldroit

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danieldroit commented Apr 3, 2019

closing the in when out gets closed:

(defn debounce [in ms]
  (let [out (chan)]
    (go-loop [last-val nil]
             (let [val   (if (nil? last-val) (<! in) last-val)
                   timer (timeout ms)
                   [new-val ch] (alts! [in timer])]
               (condp = ch
                 timer (do (when-not
                             (>! out val)
                             (close! in))
                           (recur nil))
                 in (if new-val (recur new-val)))))
    out))
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