Church-encoded JSON in F#

Json.fs

/// Church-encoded JSON values.
type Json =
    abstract Value<'r> :
            (string -> 'r)
        -> (bool -> 'r)
        -> (decimal -> 'r)
        -> (Map<string, Json> -> 'r)
        -> (List<Json> -> 'r)
        -> 'r

type ValueType = JString | JBool | JNumber | JObject | JArray

/// The type of the given JSON value.
let valueType (json : Json) : ValueType =
    json.Value (fun _ -> JString) (fun _ -> JBool) (fun _ -> JNumber) (fun _ -> JObject) (fun _ -> JArray)

/// Constructor for a JSON string.
let jsonString (s : string) : Json = { new Json with
    member _.Value isString _ _ _ _ = isString s
}
// And so on for booleans, numbers, objects and arrays.

/// Pattern match on JSON values.
let (|JString|JBool|JNumber|JObject|JArray|) (json : Json) =
    json.Value Choice1Of5 Choice2Of5 Choice3Of5 Choice4Of5 Choice5Of5 // Kind of funny

let shouldBeString =
    match jsonString "Hello" with
    | JString hello -> hello
    | _ -> failwith "Expected a string!"
// "Hello"