Elm:解析嵌套的json

import Json.Decode exposing (..)

type alias MyData =
    { id : Int
    , name : String
    , nestedData : NestedData
    }

type alias NestedData =
    { foo : String
    , bar : Int
    }

myDataDecoder : Decoder MyData
myDataDecoder =
    decode MyData
        |> required "id" int
        |> required "name" string
        |> required "nestedData" nestedDataDecoder

nestedDataDecoder : Decoder NestedData
nestedDataDecoder =
    decode NestedData
        |> required "foo" string
        |> required "bar" int

jsonString = """
    {
        "id": 1,
        "name": "John",
        "nestedData": {
            "foo": "Hello",
            "bar": 42
        }
    }
    """

result : Result String MyData
result =
    decodeString myDataDecoder jsonString