Elm examples

json.elm

import Html exposing (text)

import Json.Decode

type alias Car =
  { sensor1: Int
  , sensor2: Int
  }

type DrivingMode
  = Self
  | Record
  | Free
  
type alias Prameters =
  { mode: DrivingMode
  }

fromStringDrivingMode : String -> Json.Decode.Decoder DrivingMode
fromStringDrivingMode string =
  case string of
    "self" ->
        Json.Decode.succeed Self
    "record" ->
        Json.Decode.succeed Record
    "free" ->
        Json.Decode.succeed Free
    somethingElse ->
        Json.Decode.fail <| "Unknown theme: " ++ somethingElse


decodeDrivingMode : Json.Decode.Decoder DrivingMode
decodeDrivingMode =
  Json.Decode.string
    |> Json.Decode.andThen fromStringDrivingMode
    
parametersJsonDecoder =
  Json.Decode.map Prameters
    (Json.Decode.field "mode" decodeDrivingMode)
    
carJsonDecoder =
  Json.Decode.map2 Car
    (Json.Decode.field "sensor1" Json.Decode.int)
    (Json.Decode.field "sensor2" Json.Decode.int)
    
main =
  let
    raw_json = "{\"sensors\": {\"sensor1\": 10, \"sensor2\": 10}," ++
               " \"parameters\": {\"mode\": \"free\"}}"
  in
  let
    obj1 = (Json.Decode.decodeString (Json.Decode.at ["sensors"] carJsonDecoder) raw_json)
    obj2 = (Json.Decode.decodeString (Json.Decode.at ["parameters"] parametersJsonDecoder) raw_json)
  in
  let
        _ = Debug.log "object" obj1
        _ = Debug.log "object" obj2
  in
    text "Hello, World!"