a translation of the shapeless lens example to scalaz, https://github.com/milessabin/shapeless

FocusOnScalaz.scala

import scalaz.Lens

object FocusOnScalaz {

  // A pair of ordinary case classes ...
  case class Address(street : String, city : String, postcode : String)
  case class Person(name : String, age : Int, address : Address)

  // Some lenses over Person/Address ...
  val nameLens         = Lens.lensu[Person, String]((u, newName) => u.copy(name = newName), _.name)
  val ageLens          = Lens.lensu[Person, Int]((u, newAge) => u.copy(age = newAge), _.age)
  val addressLens      = Lens.lensu[Person, Address]((u, newAddress) => u.copy(address = newAddress), _.address)
  val addrStreetLens   = Lens.lensu[Address, String]((u, newStreet) => u.copy(street = newStreet), _.street)
  val addrCityLens     = Lens.lensu[Address, String]((u, newCity) => u.copy(city = newCity), _.city)
  val addrPostcodeLens = Lens.lensu[Address, String]((u, newCity) => u.copy(city = newCity), _.city)

  val streetLens = addrStreetLens compose addressLens
  val streetLensAlias = addrStreetLens <=< addressLens
  val streetLensAndThen = addressLens andThen addrStreetLens
  val streetLensAndThenAlias = addressLens >=> addrStreetLens

  val cityLens     = addressLens >=> addrCityLens
  val postcodeLens = addressLens >=> addrPostcodeLens

  // Starting value
  val person = Person("Joe Grey", 37, Address("Southover Street", "Brighton", "BN2 9UA"))

  // Read a field
  val age1 = ageLens get person // Type inferred is Int
  age1 == 37

  // Update a field
  val person2 = ageLens.set(person, 38)
  person2.age == 38

  // Transform a field
  val person3 = ageLens.mod(_ + 1, person2)
  person3.age == 39

  val person3s = Seq(
    (ageLens map (_ + 1)) run person2,
    (ageLens %= (_ + 1)) run person2,
    (ageLens >- (_ + 1)) run person2).unzip._1
  person3s.forall(_.age == 39)

  val nameState =
    for {
      x <- nameLens
      _ <- nameLens := x + " Eh" }
    yield x

  val (person4, _) = nameState run person
  person4.name == "Joe Grey Eh"

  // Read a nested field
  val street_ = streetLens get person3
  street_ == "Southover Street"

  // Update a nested field
  val person5 = streetLens.set(person3, "Montpelier Road")
  person5.address.street == "Montpelier Road"

  // Cumulative result of above updates
  person5 == Person("Joe Grey", 39, Address("Montpelier Road", "Brighton", "BN2 9UA"))

}