Temperature converter (ELM)

karlverter.elm

module Main exposing (main)

import Browser
import Html exposing (Html, div, h1, input, label, text)
import Html.Attributes exposing (value)
import Html.Events exposing (onInput)


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



-- MODEL


type alias Model =
    { fahrenheit : Float
    , celsius : Float
    }


myInit : Model
myInit =
    { fahrenheit = 0
    , celsius = -17.7778
    }



-- VIEW


myView : Model -> Html Msg
myView model =
    div []
        [ h1 [] [ text "Temperature converter" ]
        , div []
            [ label []
                [ text "Fahrenheit: "
                , input
                    [ value (String.fromFloat model.fahrenheit)
                    , onInput UserEnteredFahrenheit
                    ]
                    []
                ]
            ]
        , div []
            [ label []
                [ text "Celsius: "
                , input
                    [ value (String.fromFloat model.celsius)
                    , onInput UserEnteredCelsius
                    ]
                    []
                ]
            ]
        ]



-- UPDATE


type Msg
    = UserEnteredFahrenheit String
    | UserEnteredCelsius String


myUpdate : Msg -> Model -> Model
myUpdate msg model =
    case msg of
        UserEnteredFahrenheit fahrenheitString ->
            let
                fahrenheitFloat =
                    case String.toFloat fahrenheitString of
                        Nothing ->
                            0

                        Just float ->
                            float
            in
            { model
                | fahrenheit = fahrenheitFloat
                , celsius = fahrenheitToCelsius fahrenheitFloat
            }

        UserEnteredCelsius celsiusString ->
            let
                celsiusFloat =
                    case String.toFloat celsiusString of
                        Nothing ->
                            0

                        Just float ->
                            float
            in
            { model
                | celsius = celsiusFloat
                , fahrenheit = celsiusToFahrenheit celsiusFloat
            }


fahrenheitToCelsius : Float -> Float
fahrenheitToCelsius fahrenheit =
    (fahrenheit - 32) * (5 / 9)


celsiusToFahrenheit : Float -> Float
celsiusToFahrenheit celsius =
    (celsius * 9 / 5) + 32