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urfolomeus/EffectsTest.elm

Last active September 22, 2015 15:11
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EffectsTest.elm
module EffectsTest where
import Html exposing (..)
import Html.Events exposing (onClick)
import StartApp exposing (App)
import Task exposing (Task)
import Effects exposing (Effects, Never)
-- WIRING
app : App Model
app =
StartApp.start
{ init = initialModel "Hello"
, update = update
, view = view
, inputs = [incomingActions]
}
main : Signal Html
main =
app.html
port tasks : Signal (Task Never ())
port tasks =
app.tasks
-- MODEL
type alias Model = String
initialModel : String -> (Model, Effects Action)
initialModel string =
(string, Effects.none)
-- UPDATE
type Action = NoOp | RequestString | Write Model
update : Action -> Model -> (Model, Effects Action)
update action model =
case action of
NoOp ->
(model, Effects.none)
RequestString ->
(model, getNewString)
Write string ->
(string, Effects.none)
-- VIEW
view : Signal.Address Action -> Model -> Html
view address model =
div [ ]
[ text model
, button
[ onClick address RequestString ]
[ text "Click me!" ]
]
-- PORTS
port incoming : Signal Model
port outgoing : Signal String
port outgoing =
outbox.signal
-- SIGNALS
incomingActions : Signal Action
incomingActions =
Signal.map (\string -> Write string) incoming
outbox : Signal.Mailbox String
outbox =
Signal.mailbox ""
-- EFFECTS
getNewString : Effects Action
getNewString =
Signal.send outbox.address ""
|> Effects.task
|> Effects.map (always NoOp)
Raw
index.html
<!DOCTYPE html>
<html>
<head>
<title>Effects Test</title>
<script src="elm.js"></script>
</head>
<body>
<div id="elmMain"></div>
</body>
<script>
var elmDiv = document.getElementById('elmMain')
, elmApp = Elm.embed(Elm.EffectsTest, elmDiv, {incoming: ""});
elmApp.ports.incoming.send("Hello from outside");
elmApp.ports.outgoing.subscribe(function () {
elmApp.ports.incoming.send("You rang?");
});
</script>
</html>
@urfolomeus
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TL;DR
How do I deal with an Effect that needs to perform a Task but does not have an affect on the model?

I'm trying to create a basic Elm application that does the following:

  1. Accepts values from JavaScript on the incoming port, calls the Write Action in the update function and writes the given value to the View. This part works fine.
  2. Sends a message to JavaScript over the outgoing port to ask it to send a different String to the incoming port thus triggering step 1. This is the part where I am stuck.

I have a working solution that does not use Effects, but I want to be able to use StartApp so I need to work with Effects. The issue, I believe, is down to the fact that an Effect expects to have an affect on the application via a Task sent back to the update function. However I have no need to do anything as getNewString merely asks the outside world to do something. It does not wait for the response.

So, can I send back a NoOp Effect somehow? Is there a better way of doing this?

@urfolomeus
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@jessitron replied with

Signal.send outbox.address ""
  |> Effects.task
  |> Effects.map (\_ -> NoOp)

@urfolomeus
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@mgold pointed out that (\_ -> ...) is such a common pattern in Elm that there is a more common way to do it (always ...)

@urfolomeus
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Updated to show the final solution :)

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