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Let's learn Elm! 2015/07/01 @Worksap ATE Yosuke Torii

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This slide is about... - What is Elm? - Why is Elm great? - For web-app developers × Type systems × Useful tools/libraries × For game developers × For FP developers

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What's Elm? - FRP(Functional Reactive Programming) - Haskell-like Syntax - No runtime errors - Compile to JavaScript main = span [class "welcome-message"] [text "Hello, World!"]

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a = 1 b = 1 c = a + b print c // => 2 Reactive Programming

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a = 1 b = 1 c = a + b print c // => 2 b = 2 print c // => ? Reactive Programming

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Reactive Programming a b c + 1 1 2

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Reactive Programming a b c + 1 2 3

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Reactive Programming a b c + 2 2 4

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a = model(1) b = model(1) updateC = function() { c = a.value + b.value } a.onChange(updateC) b.onChange(updateC) updateC() I know the observer pattern!

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Functional Reactive Programming 2 1 Time a Signal : function of time

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Functional Reactive Programming 2 1 2 1 Time Time a b

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Functional Reactive Programming 2 1 2 1 Time Time 4 2 Time 3 1 a b c

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Basis of FRP 2 1 4 2 Time Time a b map

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Basis of FRP 3 1 Time Time a b filter 4 2 4 2

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Basis of FRP 1 1 Time Time a b scan 1 1 3 1 4 2

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Basis of FRP 1 1 Time Time a b merge 2 2 Time c 1 1 2 2

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Basis of FRP 2 1 Time Time a b lift 2 1 Time c 3 1 4 2

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FRP meets MV* architecture Action Model View
Hello, John Smith!
John Smith John Smith keydown keydown

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FRP meets MV* architecture MV* FP Elm AngularJS Backbone.js React.js Ember.js Haskell Scala OCaml LISP Erlang

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Trends of front-end MV* View Model Controller update() render()

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Trends of front-end MV* View Model Model Model View View View View View

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Trends of front-end MV* View Model Model Model View View View View View update()

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React's Virtual DOM VDOM Model Model Model DOM DOM DOM DOM VDOM VDOM VDOM

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React's Virtual DOM Model Model DOM DOM DOM DOM VDOM VDOM VDOM VDOM Model update() render()

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React's Virtual DOM Model Model DOM DOM VDOM VDOM VDOM VDOM Model update() render() DOM DOM diff exists diff exists

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Declarative programming comes back! render: function() { return (

TODO

{'Add #' + (this.state.items.length + 1)}
); }

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Frameworks that uses Virtual DOM - Mercury - Mithril - Cape.JS - Om - Elm

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Immutability makes Virtual DOM faster! Old Model DOM Old VDOM New Model DOM New VDOM diff diff

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Flux, an architecture by facebook https://github.com/facebook/flux

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Flux, an architecture by facebook https://github.com/facebook/flux one-way data flow

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Flux libraries - Fluxxor - Fluxible(by Yahoo) - RefluxJS - McFly - Delorean

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FRP libraries - Rx(C#) - RxJava(Java) - RxJS(JavaScript) - Bacon.js(JavaScript) - Sodium(Haskell) - Reative-banana(Haskell)

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FRP libraries (RxJava) http://reactivex.io/RxJava/javadoc/rx/Observable.html

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FRP libraries (RxJava) http://reactivex.io/RxJava/javadoc/rx/Observable.html

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React + X Type-safety Architecture Flux Immutability Virtual DOM Reactivilty - Flow - Bacon.js - RxJS - Fluxible - Fluxxor + α - Immutable.js

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React + X Type-safety Architecture Flux Immutability Virtual DOM Reactivilty + α ✓ ✓ ✓ ✓

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About Elm - born in Apr 2012 - ver 0.15 - designed by Evan Czaplicki (Prezi) - http://elm-lang.org/ - https://groups.google.com/forum/#! forum/elm-discuss

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About Elm 0.15 Apr 2015 Tasks, better HTTP library 0.14 Dec 2014 Package manager, parallel builds, JSON --- Jul 2014 elm-html http://evancz.github.io/elm-todomvc/ Graphics.Element Html http://elm-lang.org/examples/adventure

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Hello, world! import Html exposing (..) main : Html main = text "Hello, World!" text : String → Html

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Hello, world! import Html exposing (..) import Html.Attributes exposing (..) main : Html main = ul [class "grocery-list"] [ li [] [text "Pamplemousse"] , li [] [text "Ananas"] , li [] [text "Jus d'orange"] ] ul : List Attribute → List Html → Html li : List Attribute → List Html → Html class : String → Attribute

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Signals import Html exposing (..) import Mouse main : Signal Html main = Signal.map (\p -> text (toString p)) Mouse.position Mouse.position : Signal (Int, Int) Signal.map : (a → b) → Signal a → Signal b toString : a → String

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Signals (10, 20) Time main : Signal Html (15, 30) position : Signal (Int, Int) “(10, 20)” Time “(15, 30)” map

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Signals import Html exposing (..) import Mouse main : Signal Html main = Signal.map (\count -> text (toString count)) countClick countClick : Signal Int countClick = Signal.foldp (\clk count -> count + 1) 0 Mouse.clicks Mouse.clicks : Signal () Signal.foldp : (a → b → b) → b → Signal a → Signal b

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Signals () Time countClick : Signal Int clicks : Signal (Int, Int) Time foldp () () 1 2 3

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You might think FRP looks like...

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You might think FRP looks like... keydown timestamp errors fullname ajax formData firstName lastName enter letter tabIndex errorCount ok messages html click submit ok error reset inputs

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Actually?

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Actually? action model html

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The Elm Architecture - model - update - view http://evancz.github.io/elm-todomvc/ http://elm-lang.org/examples/adventure

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The Elm Architecture Model View Action Update Mailbox - model - update - view

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The Elm Architecture -- MODEL type alias Model = { ... } -- UPDATE type Action = Reset | ... update : Action -> Model -> Model update action model = case action of Reset -> ... ... -- VIEW view : Model -> Html view model = ...

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Code reading http://evancz.github.io/elm-todomvc/

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Model -- MODEL type alias Model = { tasks : List Task , field : String , uid : Int , visibility : String } type alias Task = { description : String , completed : Bool , editing : Bool , id : Int }

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Model newTask : String -> Int -> Task newTask desc id = { description = desc , completed = False , editing = False , id = id } emptyModel : Model emptyModel = { tasks = [] , visibility = "All" , field = "" , uid = 0 }

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Update -- UPDATE type Action = NoOp | UpdateField String | EditingTask Int Bool | UpdateTask Int String | Add | Delete Int | DeleteComplete | Check Int Bool | CheckAll Bool | ChangeVisibility String

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Update update : Action -> Model -> Model update action model = case action of NoOp -> model Add -> { model | uid <- model.uid + 1, field <- "", tasks <- if String.isEmpty model.field then model.tasks else model.tasks ++ [newTask model.field model.uid] } Delete id -> { model | tasks <- List.filter (\t -> t.id /= id) model.tasks } Check id isCompleted -> let updateTask t = if t.id == id then { t | completed <- isCompleted } else t in { model | tasks <- List.map updateTask model.tasks } ...

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View view : Address Action -> Model -> Html view address model = div [ class "todomvc-wrapper" , style [ ("visibility", "hidden") ] ] [ section [ id "todoapp" ] [ lazy2 taskEntry address model.field , lazy3 taskList address model.visibility model.tasks , lazy3 controls address model.visibility model.tasks ] , infoFooter ]

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View taskEntry : Address Action -> String -> Html taskEntry address task = header [ id "header" ] [ h1 [] [ text "todos" ] , input [ id "new-todo" , placeholder "What needs to be done?" , autofocus True , value task , name "newTodo" , on "input" targetValue (Signal.message address << UpdateField) , onEnter address Add ] [] ]

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Main main : Signal Html main = Signal.map (view actions.address) model model : Signal Model model = Signal.foldp update initialModel actions.signal actions : Signal.Mailbox Action actions = Signal.mailbox NoOp

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Good architecture makes language simple! Language Architecture ×

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Good architecture makes language simple! I want some function, but the core library doesn't support it! Q:

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Good architecture makes language simple! Is that really required? Maybe your system can be written more simply. A:

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No unnecessary features! Keep it simple. Please support monad! Q: No. A: Really need type classes! Q: No. A: Higher-kinded types... Q: No. A:

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Static graphs only Signal (Signal a)

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Static graphs only https://www.youtube.com/watch?v=Agu6jipKfYw

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Larger application

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inputView buttonView Nesting components Model View Action Mailbox

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inputView buttonView inputAction buttonAction Nesting components Model View Action Mailbox inputModel buttonModel

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Nesting components type ButtonAction = Click (Int, Int) | Hover Float | NoOp type ContainerAction = Button ButtonAction | Checkbox CheckboxAction | Inputbox InputboxAction | NoOp Button.elm Main.elm

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Nesting components type alias ContainerModel = { button : ButtonModel , input : InputModel } init : ContainerModel init = { button = Button.init , input = Input.init } Main.elm

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Nesting components containerAddress : Address ContainerAction buttonAddress : Address ButtonAction buttonAddress = Signal.forwardTo containerAddress Button checkboxAddress : Address CheckboxAction checkboxAddress = Signal.forwardTo containerAddress Checkbox inputboxAddress : Address InputboxAction inputboxAddress = Signal.forwardTo containerAddress Inputbox Main.elm

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Stateful components? 2 3 buttonA buttonB click +1

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Stateful components? updateButton : ButtonAction -> ButtonState -> ButtonState updateButton action state = case action of Click -> { state | count <- state.count + 1 } update : Action -> Model -> Model update action model = case action of ButtonA a -> { model | buttonA <- updateButton a model.buttonA } ButtonB b -> { model | buttonB <- updateButton b model.buttonB } Main.elm Button.elm

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Is Elm ready for production?

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Is Elm ready for production? Yes! But needs more libraries for productivity. type Action = Wait | Contribute

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Conclusion - Elm is a FRP language - Elm also has a good architecture - Elm is ready to use

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Thank you!