Trying to figure out why unions aren't working...

Union.elm

module Main exposing (..)

import Html exposing (Html, text, div, img)
import Html.Attributes exposing (src)


---- MODEL ----


type alias Model =
    {}


init : ( Model, Cmd Msg )
init =
    ( {}, Cmd.none )



---- UPDATE ----


type Msg
    = NoOp


update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    ( model, Cmd.none )



---- VIEW ----


type MyThing
    = AString String
    | AnInt Int
    | ATuple ( String, Int )


unionFn : MyThing -> String
unionFn thing =
    case thing of
        AString s ->
            "It was a string: " ++ s

        AnInt i ->
            "It was an int: " ++ toString i

        ATuple ( s, i ) ->
            "It was a string and an int: " ++ s ++ " and " ++ toString i


view : Model -> Html Msg
view model =
    div []
        [ text (unionFn "String") ]



---- PROGRAM ----


main : Program Never Model Msg
main =
    Html.program
        { view = view
        , init = init
        , update = update
        , subscriptions = always Sub.none
        }