gistfile1.scala

scala> :paste
// Entering paste mode (ctrl-D to finish)

case class Address(street : String, city : String, postcode : String)
case class Person(name : String, age : Int, address : Address)

// Exiting paste mode, now interpreting.

defined class Address
defined class Person

scala> import Lens._
import Lens._

scala> val ageLens = Lens[Person] >> 'age
ageLens: shapeless.Lens[Person,Int]{val gen: shapeless.LabelledGeneric[Person]{type Repr = shapeless.::[shapeless.record.FieldType[shapeless.tag.@@[Symbol,String("name")],String],shapeless.::[shapeless.record.FieldType[shapeless.tag.@@[Symbol,String("age")],Int],shapeless.::[shapeless.record.FieldType[shapeless.tag.@@[Symbol,String("address")],Address],shapeless.HNil]]]}} = shapeless.Lens$$anon$6@6eee179a

scala> val cityLens = Lens[Person] >> 'address >> 'city
cityLens: shapeless.Lens[Person,String]{val gen: shapeless.LabelledGeneric[Address]{type Repr = shapeless.::[shapeless.record.FieldType[shapeless.tag.@@[Symbol,String("street")],String],shapeless.::[shapeless.record.FieldType[shapeless.tag.@@[Symbol,String("city")],String],shapeless.::[shapeless.record.FieldType[shapeless.tag.@@[Symbol,String("postcode")],String],shapeless.HNil]]]}} = shapeless.Lens$$anon$6@30eb50db

scala> val person = Person("Joe Grey", 37, Address("Southover Street", "Brighton", "BN2 9UA"))
person: Person = Person(Joe Grey,37,Address(Southover Street,Brighton,BN2 9UA))

scala> ageLens.get(person)
res0: Int = 37

scala> ageLens.modify(person)(_+1)
res1: Person = Person(Joe Grey,38,Address(Southover Street,Brighton,BN2 9UA))

scala> cityLens.get(person)
res2: String = Brighton

scala> cityLens.set(person)("London")
res3: Person = Person(Joe Grey,37,Address(Southover Street,London,BN2 9UA))