A basic example of trying to create a schema ignorant JSON decoder in ELM

Schema.elm

import Dict exposing (Dict)
import Json.Decode as Decode

type SchemaData
    = SchemaObject (Dict String  SchemaData)
    | SchemaList (List SchemaData)
    | SchemaString String
    | SchemaInt Int
    | SchemaBool Bool
    | SchemaNull

decodeSchema : Decode.Decoder SchemaData
decodeSchema =
    Decode.oneOf
        [ Decode.keyValuePairs (Decode.lazy (\_ -> decodeSchema)) |> Decode.map makeObject
        , Decode.list (Decode.lazy (\_ -> decodeSchema)) |> Decode.map makeList
        , Decode.string |> Decode.map SchemaString
        , Decode.int |> Decode.map SchemaInt
        , Decode.bool |> Decode.map SchemaBool
        , Decode.null SchemaNull
        ]


makeList : List SchemaData -> SchemaData
makeList items =
    SchemaList items


makeObject : List ( String, SchemaData ) -> SchemaData
makeObject fields =
    SchemaObject (Dict.fromList fields)