Decoding non-trivial JSON data in Elm

Trying to decode the following JSON

[
  {
    "key": [
      "step",
      "17"
    ],
    "value": {
      "id": "1000000000",
      "active": true,
      "config": {
        "templates": {},
        "id": 17,
        "name": "Somename"
      }
    }
  },
  {
    "key": [
      "step",
      "200"
    ],
    "value": {
      "id": "1110022222",
      "active": true,
      "config": {
        "templates": {},
        "id": 200,
        "name": "something"
      }
    }
  }
]

Solution

import Graphics.Element exposing (show)
import Dict exposing (Dict)
import Json.Decode exposing (Decoder, (:=), succeed, object2, list, string, bool, dict, int, maybe, decodeString, map)
type alias Model =
 { key: List String
 , values: Value
 }
type alias Value =
 { id: String
 , active: Bool
 , config: Config
 }
type alias Config =
 { templates: Maybe (Dict String String)
 , id: Int
 , name: String
 }
 
 — Applicative’s `pure`:
constructing : a -> Decoder a
constructing = succeed
 — Applicative’s `<*>`:
apply : Decoder (a -> b) -> Decoder a -> Decoder b
apply = object2 (<|)
modelsDecoder : Decoder (List Model)
modelsDecoder = list modelDecoder
modelDecoder : Decoder Model
modelDecoder =
 constructing Model
 `apply` (“key” := list string)
 `apply` (“value” := valueDecoder)
valueDecoder : Decoder Value
valueDecoder =
 constructing Value
 `apply` (“id” := string)
 `apply` (“active” := bool)
 `apply` (“config” := configDecoder)
configDecoder : Decoder Config
configDecoder =
 constructing Config
 `apply` (“templates” := maybe (dict string))
 `apply` (“id” := int)
 `apply` (“name” := string)
jsonString = “[{\”key\”:[\”step\”,\”17\”],\”value\”:{\”id\”:\”1000000000\”,\”active\”:true,\”config\”:{\”templates\”:{},\”id\”:17,\”name\”:\”Somename\”}}},{\”key\”:[\”step\”,\”200\”],\”value\”:{\”id\”:\”1110022222\”,\”active\”:true,\”config\”:{\”templates\”:{},\”id\”:200,\”name\”:\”something\”}}}]”
main =
 case (decodeString modelsDecoder jsonString) of
 Ok value -> show value
 Err msg -> show msg

Based on:

https://gist.github.com/codedmart/69fe8adbb30298ab511c

https://gist.github.com/jamesmacaulay/c2badacb93b091489dd4