Elm // Elm Architecture

						
module Person where

import Effects exposing (Effects)
import Html exposing (button, div, pre, text, Html)
import Html.Events exposing (onClick)

-- MODEL

type alias Model =
  { age  : Int
  , kids : Int
  , name : String
  }

initialModel : Model
initialModel =
  { age  = 38
  , kids = 3
  , name = "Amitai"
  }

init : (Model, Effects Action)
init =
  ( initialModel
  , Effects.none
  )

-- UPDATE

type Action = Decrement | Increment

update : Action -> Model -> (Model, Effects Action)
update action model =
  case action of
    Decrement ->
      ( { model | kids = model.kids - 1 }
      , Effects.none
      )

    Increment ->
      ( { model | kids = model.kids + 1 }
      , Effects.none
      )

						
					

						
view : Signal.Address Action -> Model -> Html
view address model =
  div []
    [ div [] [ text <| "Name: " ++ model.name ]
    , div [] [ text <| "Age: " ++ (toString model.age) ]
    , div [] [ text <| "Kids num: " ++ (toString model.kids) ]
    , button [ onClick address Decrement ] [ text "-" ]
    , button [ onClick address Increment ] [ text "+" ]
    , pre [] [ text (toString model) ]
    ]





--
						
					

						
view : Signal.Address Action -> Model -> Html
view address model =
  div []
    [ viewName model.name
    , viewAge  model.age
    , viewKids model.age
    , button [ onClick address Decrement ] [ text "-" ]
    , button [ onClick address Increment ] [ text "+" ]
    , pre [] [ text (toString model) ]
    ]

viewName : String -> Html
viewName name =
  div [] [ text <| "Name: " ++ name ]

viewAge : Int -> Html
viewAge age =
  div [] [ text <| "Age: " ++ (toString age) ]

viewKids : Int -> Html
viewKids kids =
  div [] [ text <| "Kids num: " ++ (toString kids) ]
						
					

Compile Error Vs Runtime Error

Types 101

						
type Bool = False | True
						
					

						
type Vehicle = Boat | Plane | Car Int

type alias Model =
  { name    : String
  , vehicle : Vehicle
  }
						
					

Type Safety

						
--

type alias Model =
  { age  : Int
  , kids : Int
  , name : String
  }

initialModel : Model
initialModel =
  { age  = 38
  , kids = 3
  , name = "Amitai"
  }
						
					

						
type Kids = Kids Int

type alias Model =
  { age  : Int
  , kids : Kids
  , name : String
  }

initialModel : Model
initialModel =
  { age  = 38
  , kids = Kids 3
  , name = "Amitai"
  }

						
					

						
viewKids : Int -> Html
viewKids kids =
  div [] [ text <| "Kids num: " ++ (toString kids) ]


--
						
					

						
viewKids : Kids -> Html
viewKids kids =
  let
    (Kids val) = kids
  in
    div [] [ text <| "Kids num: " ++ (toString val) ]
						
					

						
update : Action -> Model -> (Model, Effects Action)
update action model =
  case action of
    Decrement ->
      ( { model | kids = model.kids - 1 }
      , Effects.none
      )

    Increment ->
      ( { model | kids = model.kids + 1 }
      , Effects.none
      )




--
						
					

						
update : Action -> Model -> (Model, Effects Action)
update action model =
  case action of
    Decrement ->
      let
        (Kids val) = model.kids
        kids' = Kids (val - 1)
      in
        ( { model | kids = kids' }
        , Effects.none
        )

    Increment ->
      let
        (Kids val) = model.kids
        kids' = Kids (val + 1)
      in
        ( { model | kids = kids' }
        , Effects.none
        )
						
					

Business logic from the Data level

						
update : Action -> Model -> (Model, Effects Action)
update action model =
  case action of
    Decrement ->
      let
        (Kids val) = model.kids
        kids' = Kids (val - 1)
      in
        ( { model | kids = kids' }
        , Effects.none
        )

    Increment ->
      let
        (Kids val) = model.kids
        kids' = Kids (val + 1)
      in
        ( { model | kids = kids' }
        , Effects.none
        )
						
					

						
update : Action -> Model -> (Model, Effects Action)
update action model =
  case action of
    Decrement ->
      let
        (Kids val) = model.kids
        kids' = if val < 1 then Kids 0 else Kids (val - 1)
      in
        ( { model | kids = kids' }
        , Effects.none
        )

    Increment ->
      let
        (Kids val) = model.kids
        kids' = if val > 4 then Kids 5 else Kids (val + 1)
      in
        ( { model | kids = kids' }
        , Effects.none
        )
						
					

Buisness Logic requires Testing

						
decrementActionSuite : Test
decrementActionSuite =
  suite "Decerment action"
    [ test "zero count" (assertEqual 0 (updateKids Person.Decrement 0))
    , test "positive count" (assertEqual 0 (updateKids Person.Decrement 1))
    , test "top limit count" (assertEqual 4 (updateKids Person.Decrement 5))
    ]
						
					

						
suite "Decerment action"
	[ test "negative count" (assertEqual 0 1)
	]
						
					

						
decrementActionSuite : Test
decrementActionSuite =
  suite "Decerment action"
    -- Kids = 0 -> Kids = 0
    [ test "zero count" (assertEqual 0 (updateKids Person.Decrement 0))
    -- Kids = 1 -> Kids = 0
    , test "positive count" (assertEqual 0 (updateKids Person.Decrement 1))
    -- Kids = 5 -> Kids = 4
    , test "top limit count" (assertEqual 4 (updateKids Person.Decrement 5))
    ]

updateKids : Person.Action -> Int -> Int
updateKids action initialKids =
  let
    model = { initialModel | kids = (Person.Kids initialKids) }
    model' = fst <| Person.update action model
    (Person.Kids kids') = model'.kids
  in
    kids'