A snippet for making a `Json.Decoder` from a result

ElmTurnResultIntoDecoder.elm

-- From https://robots.thoughtbot.com/5-common-json-decoders#1---decoding-union-types

fromResult : Result String a -> Decoder a
fromResult result =
  case result of
    Ok a -> JD.succeed a
    Err errorMessage -> JD.fail errorMessage


parseDirection : String -> Result String Direction
parseDirection string =
  case string of
    "north" -> Ok North
    "south" -> Ok South
    "east" -> Ok East
    "west" -> Ok West
    _ -> Err ("Invalid direction: " ++ string)


direction : Decoder Direction
direction =
  Decode.string |> Decode.andThen (fromResult << parseDirection)
  
  
date : Decoder Date
date =
  Decode.string |> Decode.andThen (fromResult << Date.fromString)