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Sequential computation macro #148

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chr15m opened this issue Dec 17, 2023 · 1 comment
Open

Sequential computation macro #148

chr15m opened this issue Dec 17, 2023 · 1 comment

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@chr15m
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chr15m commented Dec 17, 2023

It would be great if there was a way to run a series of promises sequentially, waiting for the previous one to finish, and return a vec of all promises for use with p/all. This is different to creating a map of promise returning functions as that would run in parallel not sequentially. See discussion on Slack here.

Here is an implementation using reduce:

(p/let [result
          (p/all
            (reduce
              (fn [col panel-choice]
                (conj col
                      (p/let [_ (last col)]
                        (something-returning-promise panel-choice))))
              []
              panel-choices))]
    (print "reduce" result))

Here is an implementation using p/loop and p/recur:

(p/let [result
          (p/loop [choices panel-choices results []]
            (if (empty? choices)
              results
              (p/let [result (something-returning-promise
                               (first choices))]
                (p/recur (rest choices)
                         (conj results result)))))]
    (print "loop/recur" result))

You can test this in nbb with promises.cljs here:
https://gist.github.com/chr15m/c5f943b6aa2c6089c04f04897b3cef81
@chr15m chr15m changed the title Sequential computation option Sequential computation macro Dec 17, 2023
@niwinz
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niwinz commented May 12, 2025

That is interesting, but after looking a referenced gist, I see a very different set of operations and each one has its own use cases and its own impl. Is not the same if you want collect the results (aka reduce-like) or just need to execute N number of tasks secuentially without collecting the result.
Can we elaborate a bit the real needed use case?

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