precedencegroup FunctionComposition {
  associativity: right
  higherThan: LensGetter
}

precedencegroup FunctionApplication {
  associativity: left
}

precedencegroup LensSetter {
  associativity: right
  higherThan: FunctionApplication
}

precedencegroup LensGetter {
  associativity: right
  higherThan: LensSetter
}

infix operator |>: FunctionApplication
infix operator %~: LensSetter
infix operator .~: LensSetter

infix operator .^: LensGetter

func |> <A, B>(x: A, f: (A) -> B) -> B {
  return f(x)
}

public protocol LensProtocol {
  associatedtype Root
  associatedtype Value
  var get: (Root) -> Value { get }
  var set: (Root, Value) -> Root { get }
}

public struct Lens<Root, Value>: LensProtocol {
  public let get: (Root) -> Value
  public let set: (Root, Value) -> Root
}

extension WritableKeyPath: LensProtocol {
  public var get: (Root) -> Value {
    return { root in root[keyPath: self] }
  }

  public var set: (Root, Value) -> Root {
    return { root, value in
      var copy = root
      copy[keyPath: self] = value
      return copy
    }
  }
}

public func .~ <L: LensProtocol>(lens: L, value: L.Value) -> (L.Root) -> L.Root {
  return { root in lens.set(root, value) }
}

public func %~ <L: LensProtocol>(lens: L, over: @escaping (L.Value) -> L.Value) -> (L.Root) -> L.Root {
  return { root in lens.set(root, over(lens.get(root))) }
}

public func .^ <L: LensProtocol>(root: L.Root, lens: L) -> L.Value {
  return lens.get(root)
}

struct User {
  private(set) var id: Int
  private(set) var name: String

  public init(id: Int, name: String) {
    self.id = id
    self.name = name
  }
}

let incr: (Int) -> Int = { $0 + 1 }
let uppercased: (String) -> String = { $0.uppercased() }

let user = User(id: 1, name: "Stephen")

user
  |> \.id %~ incr
  |> \.name %~ uppercased

precedencegroup FunctionComposition {
  associativity: right
  higherThan: LensGetter
}

precedencegroup FunctionApplication {
  associativity: left
}

precedencegroup LensSetter {
  associativity: right
  higherThan: FunctionApplication
}

precedencegroup LensGetter {
  associativity: right
  higherThan: LensSetter
}

infix operator |>: FunctionApplication
infix operator %~: LensSetter
infix operator .~: LensSetter

infix operator .^: LensGetter

func |> <A, B>(x: A, f: (A) -> B) -> B {
  return f(x)
}

public func %~ <Root, Value>(path: KeyPath<Root, Value>, over: @escaping (Value) -> Value) -> (Root) -> Root {
  return { root in
    let writablePath = path as! WritableKeyPath<Root, Value>
    var copy = root
    copy[keyPath: writablePath] = over(copy[keyPath: writablePath])
    return copy
  }
}

public func .~ <Root, Value>(path: KeyPath<Root, Value>, value: Value) -> (Root) -> Root {
  return path %~ const(value)
}

struct User {
  private(set) var id: Int
  private(set) var name: String

  public init(id: Int, name: String) {
    self.id = id
    self.name = name
  }
}

let incr: (Int) -> Int = { $0 + 1 }
let uppercased: (String) -> String = { $0.uppercased() }

let user = User(id: 1, name: "Stephen")

user
  |> \.id %~ incr
  |> \.name %~ uppercased

user
  |> \User.id %~ incr
  |> \User.name %~ uppercased