elm-every's Introduction

Elm-Every

Repeatidly issue an action, with some time frame in-between.

It's pretty simple to integrate, all you need is:

a function to determine how much time to wait until the next issue, based on the total time waited so far: Time -> Time
an action to issue, with some data it would expect to apply with

Then, to start the poller, you issue Start with some data you would want the action to use. To update this data, just make another call to Start. Then, to stop the poller, just issue Stop.

import Every


type alias EveryState =
  { kickoffCount : Int
  }

type alias MyModel =
  { mySession : SessionModel
  , poller    : Every.Model EveryState
  }

initMyModel : MyModel
initMyModel =
  { mySession = initSession
  , poller    = Every.init
  }

type MyAction
  = SessionMsg SessionMsg
  | EveryMsg (Every.Msg EveryState)
  | KickStart

-- we're calculating the time to add to the total, based on the current total.
fibbDelay : Maybe EveryState -> Time -> Time
fibbDelay _ total = total

issueMsg : Maybe EveryState -> Msg
issueMsg ms =
  -- ...


updateModel : MyAction
           -> MyModel
           -> (MyModel, Cmd MyAction)
updateModel action model =
  case action of
    SessionMsg a ->
      let (newSession, eff) = updateSession a model.mySession
      in  ( { model | mySession = newSession }
          , Cmd.map SessionMsg eff
          )
    EveryMsg a ->
      let (newEvery, eff) = updateEvery
                              fibbDelay
                              issueMsg
                              a
                              model.poller
      in  ( { model | poller = newEvery }
          , Cmd.map (\r -> case r of
                             Err x -> x -- resolve issued data
                             Ok  x -> EveryMsg x) eff
          )
    KickStart ->
      ( model
      , Task.perform (Debug.crash << toString) EveryMsg
        <| Every.Start { resetSoFar = True
                       , modifyData = Just <| Every.Update <| \ms ->
                           case ms of
                             Nothing ->
                               { kickoffCount = 1
                               }
                             Just ks ->
                               { kickoffCount = ks.kickoffCount + 1
                               }
                       }
      )

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