HelloWorld.elm

import Html exposing (Html, Attribute, input, strong, ul, li, em, div, text, button)
import Html.App as Html
import Html.Attributes exposing (..)
import Html.Events exposing (onInput, onClick)

main =
    Html.beginnerProgram { model = model, view = view, update = update }


-- MODEL

type alias Model = 
    { subject : String
    , previous: List String
    }

model : Model
model = 
    { subject = ""
    , previous = ["World", "Earth"]
    }


-- UPDATE

-- Delegates
type Message
    = ReplaceSubject String
    | AddItem

-- Something like Message<Model in, Model out>
update : Message -> Model -> Model
update message model =
    case message of 
        ReplaceSubject newMessage -> 
            { model | subject = newMessage }
        AddItem -> 
            { model | previous = model.subject :: model.previous}


-- VIEW

prevEls previous = 
    let 
        children = List.map prevItem previous
    in 
        ul [] children

prevItem item =
    li [] [ text item ]

view : Model -> Html Message
view model = 
    div [] [ 
        div [] 
            [ input [placeholder "Placeholder", onInput ReplaceSubject] [text model.subject]
            , button [onClick AddItem] [text "Add"]
            ]
        , div [] 
            [ prevEls model.previous
            ]
        , div []
            [ strong [] [text "Hello"]
            , em [] [text model.subject ]
            ]
    ]