Prototype.elm

module Data.Thing
    exposing 
        ( Thing
        , decoder
        , encoder
        )

import Json.Encode as Encode exposing (Value)
import Json.Decode as Decode exposing (Decoder)


type Thing
    = Thing


encode : Thing -> Value
encode thing =
    Encode.string "thing"


decoder : Decoder Thing
decoder =
    Decode.string
        |> Decode.andThen toThingDecoder


toThingDecoder : String -> Decoder Thing
toThingDecoder str =
    case str of
        "Thing" ->
            Decode.succeed Thing

        _ ->
            Decode.fail "Not a thing"