Elm code for parsing json data

Main.elm

module Main exposing (..)

import Html exposing (Html, text, div, h1, img, p, ul, li, hr)
import Html.Attributes exposing (src)
import Json.Decode exposing (..)
import ISO8601


---- MODEL ----


type alias Flags =
    { population_id : Int
    , token : String
    }


type alias Model =
    { id : Int
    , token : String
    }


init : Flags -> ( Model, Cmd Msg )
init flags =
    ( { id = flags.population_id
      , token = flags.token
      }
    , Cmd.none
    )


type alias Data =
    { id : Int, results : List JsonResult }


dataDecoder =
    map2 Data (field "id" int) (field "results" (list resultDecoder))


type alias JsonResult =
    { population_id : Int
    , concentration : Float
    , created_at : ISO8601.Time
    , updated_at : ISO8601.Time
    }


resultDecoder =
    map4 JsonResult
        (field "population_id" int)
        (field "concentration" float)
        (field "created_at" decodeTimeStamp)
        (field "updated_at" decodeTimeStamp)


decodeTimeStamp : Decoder ISO8601.Time
decodeTimeStamp =
    string
        |> andThen
            (\val ->
                (case (ISO8601.fromString val) of
                    Ok ts ->
                        Json.Decode.succeed ts

                    Err errmsg ->
                        Json.Decode.fail errmsg
                )
            )


sampleData =
    """{"id":1,"results":[{"id":1,"population_id":1,"concentration":4.856980400767765,"created_at":"2018-08-14T12:00:00.000Z","updated_at":"2018-08-14T12:00:00.000Z"},{"id":2,"population_id":1,"concentration":5.18766176298193,"created_at":"2018-08-11T15:00:00.000Z","updated_at":"2018-08-11T15:00:00.000Z"},{"id":3,"population_id":1,"concentration":7.052054290295231,"created_at":"2018-08-10T10:00:00.000Z","updated_at":"2018-08-10T10:00:00.000Z"}]}"""



---- UPDATE ----


type Msg
    = NoOp


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



---- VIEW ----


boo res =
    case res of
        Err msg ->
            []

        Ok a ->
            a.results


view : Model -> Html Msg
view model =
    let
        res =
            (decodeString dataDecoder model.token)
    in
        div []
            [ h1 [] [ text "Your Elm App is working! almost fairly flawlessly" ]
            , p [] [ text (toString model) ]
            , p [] [ text (toString res) ]
            , Html.hr [] []
            , toHtmlList (boo res)
            ]


toHtmlList : List JsonResult -> Html msg
toHtmlList strings =
    ul [] (List.map toLi strings)


toLi : JsonResult -> Html msg
toLi s =
    li []
        [ text
            ("concentration "
                ++ (toString s.concentration)
                ++ " date converted back to string "
                ++ (ISO8601.toString s.created_at)
            )
        ]



---- PROGRAM ----


main =
    Html.programWithFlags
        { view = view
        , init = init
        , update = update
        , subscriptions = always Sub.none
        }

show.html.erb

<div id="elmdiv"></div>

<script>
 var node = document.getElementById('elmdiv');
 var app = Elm.Main.embed(node, {
   population_id: <%= @population.id %>,
   token: '<%= raw @population.samples.to_json %>'
 });
 // Note: if your Elm module is named "MyThing.Root" you
 // would call "Elm.MyThing.Root.embed(node)" instead.
</script>