lenstype.swift

protocol LensType {
  typealias Whole
  typealias Part
  var get: Whole -> Part { get }
  var set: (Part, Whole) -> Whole { get }
}

struct Lens <A, B> : LensType {
  typealias Whole = A
  typealias Part = B
  let get: A -> B
  let set: (B, A) -> A
}


extension LensType where Whole == User, Part == Location {
  var _name: Lens<User, String> {
    return Lens(
      get: { user in self.get(user).name },
      set: { (name, user) in User._location.set(Location._name.set(name, self.get(user)), user) }
    )
  }
}
extension LensType where Whole == Project, Part == Location {
  var _name: Lens<Project, String> {
    return Lens(
      get: { project in self.get(project).name },
      set: { (name, project) in Project._location.set(Location._name.set(name, self.get(project)), project) }
    )
  }
}
extension LensType where Whole == Project, Part == User {
  var _name: Lens<Project, String> {
    return Lens(
      get: { project in self.get(project).name },
      set: { (name, project) in Project._creator.set(User._name.set(name, self.get(project)), project) }
    )
  }
  var _location: Lens<Project, Location> {
    return Lens(
      get: { project in self.get(project).location },
      set: { (location, project) in Project._creator.set(User._location.set(location, self.get(project)), project) }
    )
  }
}

let schema = Project._location._name *~ "LA"
  |> Project._creator._name *~ "Joel Hodgson"
  |> Project._creator._location._name *~ "New York"

mst3k |> schema