Highway

to

Elm

Highway

to

Elm

https://github.com/jgrenat/elm-workshop

Jordane Grenat

@JoGrenat

Front-end is dominated by

JavaScript is backward compatible

Biggest advantage

Biggest disadvantage

You can't deprecate things !!! 😱

null > 0  // false

null == 0 // false

null >= 0 // ... true

JS syntax size

Time

ES6

A LOT to learn!

  • The language is complex
  • Many ways to do the same thing
  • Framework choice / learning
  • Tooling

Hard to optimize

  • Dead code elimination / Tree shaking
  • Assets size
  • Complex build

Low confidence level

  • Minor IDE assistance
  • Refactoring is painful
  • Slow feedback cycle: runtime
  • Dependencies are risky

Elm is a typed functional language to create fast and reliable web applications

Websites and webapps

Domain specific

Statically typed

  • Many bugs don't compile
  • IDE can help you
  • Refactoring is compiler-driven
  • Feedback cycle is really fast

No Runtime Exceptions

17K+ LoC

200K+ LoC

Fast

  • Everything is pure => optimizations
  • Small assets

"Elm has a very strong emphasis on simplicity, ease-of-use, and quality tooling."

Simplicity, ease of use

  • Focused on one purpose
  • Syntax removal
  • Well-thought API
  • Compiler helps you
  • Explicitness

Quality tooling

  • Compiler
  • Project starter
  • Package manager
  • Dev environment
  • REPL
  • Tests runner
  • Doc tool

Great community

See also Building Trust: What Has Worked by Richard Feldman 

and What is success? by Evan Czaplicki

Syntax

-- a single line comment

{- a 
   multiline 
   comment
-}

Comments

Modules

module Map exposing (navigate)

import Random
import Html exposing (div, h1)
myString : String
myString = "Hello"


add : Int -> Int -> Int
add a b = a + b

Type annotations

myUser : { login : String, password : String }
myUser = { login = "Jordane", password = "passw0rd" }


updatedUser = 
    { myUser | password = "S3cur3d" }

-- { login = "Jordane", password = "S3cur3d" }

Record update

let





in
  twentyFour + sixteen
3 * 8 + 4 * 4





let
  twentyFour =
    3 * 8

  sixteen =
    4 * 4
in
  twentyFour + sixteen

let ... in

case myNumber of
    0 ->
        "Zero"
    1 -> 
        "One"
    anythingElse -> 
        "Nor 0 nor 1"

case ... of

case myNumber of
    0 ->
        "Zero"
    1 -> 
        "One"
    _ -> 
        "Nor 0 nor 1"
case myStringMaybe of
    Just myString ->
        "myStringMaybe contains: " ++ myString
    Nothing ->
        "myStringMaybe contains nothing"

case ... of

myStringMaybe = Just "Hello"
"Hello"
case myList of
    [] ->
        "The list is empty"
    firstElement :: tail ->
        "First element: " ++ firstElement

case ... of

myList = ["first", "second", "third"]
"first"
["second", "third"]

What we'll build

The
Elm
Architecture

Model

view()

update()

Html Msg

Elm Runtime

Msg

Html

Event

(new) Model

Program: Sandbox

main : Program () Model Msg
main = 
    Browser.sandbox
        { init = initialModel, view = view, update = update }
main : Program () Model Msg
main = 
    Browser.sandbox
        { init = initialModel, view = view, update = update }

type alias Model = { counterValue : Int }

main : Program () Model Msg
main = 
    Browser.sandbox
        { init = initialModel, view = view, update = update }

type alias Model = { counterValue : Int }

view : Model -> Html Msg
view model = 
    -- Display view according to model

main : Program () Model Msg
main = 
    Browser.sandbox
        { init = initialModel, view = view, update = update }

type alias Model = { counterValue : Int }

view : Model -> Html Msg
view model = 
    -- Display view according to model

type Msg = 
    Increment | Decrement

main : Program () Model Msg
main = 
    Browser.sandbox
        { init = initialModel, view = view, update = update }

type alias Model = { counterValue : Int }

view : Model -> Html Msg
view model = 
    -- Display view according to model

type Msg = 
    Increment | Decrement

update : Msg -> Model -> Model
update msg model = 
    -- Return new model according to message and former model

Program: Sandbox

update : Msg -> Model -> Model
update msg model = 
    case msg of 
        Increment ->
            { model | counterValue = model.counterValue + 1 }

        Decrement ->
            { model | counterValue = model.counterValue - 1 }

Shuffle answers

shuffleAnswers answers
-- ["Rouge", "Noir", "Blanc", "Vert"]

shuffleAnswers answers
-- ["Noir", "Blanc", "Vert", "Rouge"]

Ask the Elm Runtime to do it!

Effects

Model

view()

update()

Html Msg

Elm Runtime

Msg

Model

Model

Msg

Cmd Msg

Program: Element

main : Program Value Model Msg
main = 
    Browser.element 
        { init = init
        , view = view
        , update = update
        , subscriptions = subscriptions
        }

main : Program Value Model Msg
main = 
    Browser.element 
        { init = init
        , view = view
        , update = update
        , subscriptions = subscriptions
        }

init : Value -> (Model, Cmd Msg)

main : Program Value Model Msg
main = 
    Browser.element 
        { init = init
        , view = view
        , update = update
        , subscriptions = subscriptions
        }

init : Value -> (Model, Cmd Msg)

update : Msg -> Model -> (Model, Cmd Msg)
main : Program Value Model Msg
main = 
    Browser.element 
        { init = init
        , view = view
        , update = update
        , subscriptions = subscriptions
        }

init : Value -> (Model, Cmd Msg)

update : Msg -> Model -> (Model, Cmd Msg)

subscriptions : Model -> Sub Msg

Random

  • Take this question
  • Get all the answers
  • Pick them in a random order
  • Put them in the question

Runtime

Generator Question

Cmd Msg

Random

type Msg = 
    GenerateInt
    | IntGenerated Int


update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of 
        GenerateInt -> 
            ( model, Random.generate IntGenerated Random.int )

        IntGenerated int -> 
            ( { model | randomInt = int }, Cmd.none )

Generator Int

Cmd Msg

Advantages

  • Great developer experience
  • No runtime exceptions
  • Great debugger
  • Powerful type system
  • Great performances
  • Great community

Drawbacks

  • Opinionated governance model
  • Boilerplate vs Explicitness
  • Not for every use case

Why use Elm?

  • Complex UI / Model
  • Frequent refactoring
  • You care for bugs
  • Easy introduction to FP
  • Write better code

Thank you!

Links

Slides : http://bit.ly/elmlang-workshop

Official website: elm-lang.org

The game: trivia-game.surge.sh

Workshop: github.com/jgrenat/elm-workshop 

Awesome talks:

 

Workshop – Highway to Elm!

By ereold

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Workshop – Highway to Elm!

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