Task requests and tracking progress #61

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1. jaredramirez commented on Sep 23, 2019

   

   jaredramirez

   on Sep 23, 2019

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   Maybe relevant: https://discourse.elm-lang.org/t/upload-files-to-s3/4314/14?u=jaredramirez
2. lydell commented on Nov 1, 2019

   

   lydell

   on Nov 1, 2019

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   Here’s a use case.

   I made a function that first asks my API for an AWS S3 signed URL, and then uploads a file to that signed URL (using Task.andThen). Now I wanted to show the upload progress, but learned that Http.task does not take a tracker. It felt nice having a function that let me upload a file without having to think about the presigned URL, but now I have to break it up into two steps and use Http.request instead.

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3. toastal commented on Jan 6, 2020

   

   toastal

   on Jan 6, 2020

   Last edited by toastal

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   Use case 2:

   I wanted a waitAtLeast function for my form submissions because sometimes that request would react before the user knew, additionally sometimes I raise a toast on the screen and don't want it to popup and disappear too quickly if the request is fast. If Cmd/Tasks were like Futures, I'd run a timer and the request in parallel and await both the results (ditching the timer) Parallelism isn't really supported in that sort of way. To get around that, I've used Task.andThen like:

   waitAtLeast : Int -> Task x a -> Task x a
   waitAtLeast delay task =
       -- Sure would be nice to have do notation here
       -- do
       --   start <- Time.now
       --   value <- task
       --   end <- Time.now
       --   let toWait = end - start - delay
       -- . . .
       -- desugared into:
       Time.now
           |> Task.andThen
               (\start ->
                   task
                       |> Task.andThen
                           (\value ->
                               Time.now
                                   |> Task.andThen
                                       (\end ->
                                           let
                                               toWait : Int
                                               toWait =
                                                   delay
                                                       - Time.posixToMillis end
                                                       + Time.posixToMillis start
                                           in
                                           if toWait <= 0 then
                                               Task.succeed value
   
                                           else
                                               Process.sleep (toFloat toWait)
                                                   |> Task.andThen (\_ -> Task.succeed value)
                                       )
                           )
               )

   Turning a Http.Request into a Task, I get the waitAtLeast part I wanted, but now that it's a Task I have no access to the tracker.
4. jjant commented on Sep 29, 2021

   

   jjant

   on Sep 29, 2021

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   @evancz ?

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