Related blog post: http://bhargavg.com/swift/2016/03/30/json-parsing-with-value-transformers.html

Curries.swift

func makePerson(name: String) -> (age: Int) -> (status: MaritalStatus) -> (requestIDs: [Int]) -> (address: Address) -> Person {
    return { age in { status in { requestIDs in { address in
        Person(name: name, age: age, status: status, requestIDs: requestIDs, address: address)
        }}}}
}

func makeAddress(flatNo: String) -> (buildingName: String) -> Address {
    return { buildingName in
        Address(flatNo: flatNo, buildingName: buildingName)
    }
}

Functions.swift

func get<T, U>(box:[String: U], key: String) -> T? {
    return box[key] as? T
}

main.swift

let json: [String: Any] = [
    "name": "Bill",
    "age": 47,
    "status": "s",
    "request_ids": [178, 249, 320, 4481],
    "address": [
        "flat_no": "31/c",
        "building_name": "Grand Arcade"
    ],
]

func parseAddress(dict: [String: String]) -> Address? {
    return makeAddress <*> get(dict, key: "flat_no")
                       <*> get(dict, key: "building_name")
}

func parseStatus(value: String) -> MaritalStatus? {
    switch value {
    case "s":
        return .Single
    case "m":
        return .Married
    default:
        return .None
    }
}


func parsePerson<T>(dict: [String: T]) -> Person? {
    return makePerson <*> get(dict, key: "name")
                      <*> get(dict, key: "age")
                      <*> get(dict, key: "status")  <~~ parseStatus
                      <*> get(dict, key: "request_ids")
                      <*> get(dict, key: "address")  <~~ parseAddress
}

print(parsePerson(json)!)

Models.swift

struct Person {
    let name: String
    let age: Int
    let status: MaritalStatus
    let requestIDs: [Int]
    let address: Address
}

struct Address {
    let flatNo: String
    let buildingName: String
}

enum MaritalStatus {
    case Married, Single
}

Operators.swift

infix operator <*> {
    associativity left
    precedence 100
}

// Operator that takes
//     f: An optional function that takes A and returns B
//     x: An optional value of type A
//
// and returns f(x) if both f and x are present
func <*><A, B>(f: (A -> B)?, x: A?) -> B? {
    guard let f = f, x = x else {
        return nil
    }
    return f(x)
}

infix operator <~~ {
    associativity left
    precedence 110  // higher than <*> precedence
}

// Operator that takes
//      x: Optional value of type A
//      f: Transformation function that maps from
//         A to an Optional B (because the transformation can fail)
//
// and returns f(x) if x is present (applies the transformation)
func <~~<A, B>(x: A?, f: (A -> B?)) -> B? {
    guard let x = x else {
        return .None
    }
    return f(x)
}