add num1 num2 = num1 + num2
sayWoof animal = animal ++ " says woof!"

--

add 3 3 -- 6
sayWoof "cat" -- "cat says woof!"

function add(num1, num2) {
  return num1 + num2;
}
function sayWoof(animal) {
  return `${animal} says woof!`;
}

// --

add(3, 3) // 6
sayWoof('cat') // 'cat says woof!'

mutateMe = 7
mutateOutside = mutateMe + 1

--

mutateOutside -- 8
mutateMe -- 7
-- NO MECHANISM TO CHANGE OUTSIDE VARS!

let mutateMe = 7;
function mutateOutside() {
  mutateMe++;
  return mutateMe;
}

// --

mutateOutside() // 8
mutateMe // 8
// OH NOES, SIDE EFFECT!

priceList =
    [1, 2, 3, 4]


makeProfit price =
    price * 1.5


markupInventory list =
    List.map makeProfit list

--

markupInventory priceList -- 1.5, 3, 4.5, 6

const priceList = [1, 2, 3, 4];

function markupInventory(list) {
  const profitList = [];
  const length = list.length;

  for (let i = 0; i < length; i++) {
    profitList.push(list[i] * 1.5);
  }

  return profitList;
}

// --

markupInventory(priceList); // [1.5, 3, 4.5, 6]

babyAnimals a b =
    "i love " ++ a ++ " and " ++ b

babyKoalas = babyAnimals "koalas"

--

babyKoalas "puppies" -- "i love koalas and puppies"
babyKoalas "kittens" -- "i love koalas and kittens"
babyKoalas "pandas" -- "i love koalas and pandas"

--

babyAnimals "koalas" "kittens"
-- "i love koalas and kittens"

function babyAnimals(a) {
  return function(b) {
    return `i love ${a} and ${b}`;
  }
}

const babyKoala = babyAnimals('koalas');

//

babyKoala('puppies'); // 'i love koalas and puppies'
babyKoala('kittens'); // 'i love koalas and kittens'
babyKoala('pandas'); // 'i love koalas and pandas'

//
babyAnimals('koalas')('kittens');
// 'i love koalas and kittens'

list =
    List.range 1 5

list
    |> List.map (\n -> n * 2) -- [2,4,6,8,10]
    |> List.filter (\n -> n > 6) -- [8,10]
    |> List.map (\n -> n * n) -- [64,100]

import _ from 'lodash';

const list = _.range(1, 6);

_
  .chain(list)
  .map(n => n * 2) // [2,4,6,8,10]
  .filter(n => n > 6) // [8,10]
  .map(n => n * n) // [64,100]
  .value() // [64,100]

-- Values

amBald : Bool
amBald = True

catNoise : String
catNoise = "meow"

nums : List Int
nums = [1, 2, 3]

-- Functions

sayMeow : String -> String
sayMeow animal =
    animal ++ " says meow"

add : Int -> Int -> Int
add x y =
    x + y

> sayMeow 19
-- TYPE MISMATCH --------------------------------------------- repl-temp-000.elm

The argument to function `sayMeow` is causing a mismatch.

3|   sayMeow 19
             ^^
Function `sayMeow` is expecting the argument to be:

    String

But it is:

    number

type Disposition = Surly | Friendly | Ambivalent
type alias Cat = {
    name: String, 
    weight: Float, 
    disposition: Disposition 
    }

seamus : Cat
seamus =
    { name = "Seamus"
    , weight = 22.2
    , disposition = Surly
    }

--

seamus.name -- "Seamus"
seamus.weight -- 22.2
.name seamus -- "Seamus"

// Flow + Webpack + Babel config required!

/*@flow*/

type Disposition = 'Surly' | 'Friendly' | 'Ambivalent'

type Cat = {
  name: string,
  weight: number,
  disposition: Disposition,
};


const seamus: Cat = {
  name: 'Seamus',
  weight: 22.2,
  disposition: 'Surly',
};

type Disposition = Surly | Friendly | Ambivalent
type alias Cat = {
    name: String, 
    weight: Float, 
    disposition: Disposition 
    }

seamus = Cat "Seamus" 22.2 Surly
debris = Cat "Debris" 9.1 Friendly
simone = Cat "Simone" 7.2 Ambivalent

--

piggySeamus = { seamus | weight = seamus.weight * 1.1 }

piggySeamus.weight -- 24.42 : Float
seamus.weight -- 22.2 : Float

type Disposition
    = Surly
    | Friendly
    | Ambivalent
    | Mix Disposition Disposition

-- type alias Cat = { ...

seamus = Cat "Seamus" 22.2 Surly
debris = Cat "Debris" 9.1 Friendly
simone = Cat "Simone" 7.2 (Mix Ambivalent Surly)

-- Special type built in to Elm

type Maybe a -- "a" here means "anything"
    = Just a -- "Just have a user, Cat, value"
    | Nothing -- "Or I don't have anything"

--

type alias User =
  { name : String
  , age : Maybe Int
  }

sue : User
sue =
  { name = "Sue", age = Nothing }

tom : User
tom =
  { name = "Tom", age = Just 24 }

canBuyAlcohol : User -> Bool
canBuyAlcohol user =
  case user.age of
    Nothing ->
      False
    Just age ->
      age >= 21
--
canBuyAlcohol tom -- True
canBuyAlcohol sue -- False
--

myList : List String                      
myList = ["First", "Second"]         

-- List.head : List a -> Maybe.Maybe a

case List.head myList of                  
  Nothing ->                              
    "Empty list!"

  Just val ->                             
    val

-- List.head myList returns a Maybe, NOT value

let myList = ['First', 'Second'];

myList[0]; // "First"

let myList = [];

myList[0]; // undefined, *KABOOOOOOM*

--
getRandomGif : String -> Cmd Msg
getRandomGif topic =
    let
        url =
            "https://api.giphy.com/v1/..." ++ topic
    in
    Http.send NewGif (Http.get url decodeGifUrl)

--
decodeGifUrl : Decode.Decoder String
decodeGifUrl =
    Decode.at [ "data", "image_url" ] Decode.string

update : Msg -> Model -> (Model, Cmd Msg)
update msg model =
  case msg of
    MorePlease ->
      (model, getRandomGif model.topic)

    NewGif (Ok newUrl) ->
      (Model model.topic newUrl, Cmd.none)

    NewGif (Err _) ->
      (model, Cmd.none)

elm-make src/Main.elm --output=build/main.js

<script src="build/main.js"></script>
<script>
  const node = document.getElementById('main');
  const app = Elm.Main.embed(node);
</script>