Lensed

lensed.scala

// see https://github.com/gseitz/Lensed

case class CoState[A, B](put: A => B, pos: A)

object CoState {
  type Store[A, B] = CoState[A, B]
}

// fused get/set
case class Lens[A, B](lens: A => CoState[B, A]) {
  def get(a: A): B = lens(a).pos

  def set(a: A): B => A = lens(a).put
}

object Lensed {

  import scalaz._
  import Scalaz._

  case class Address(street: String)

  case class Person(name: String, address: Address)

  object Person {
    // currently generated
    val name: Lens[Person, String] = Lens(_.name, (p, n) => p.copy(name = n))
    val address: Lens[Person, Address] = Lens(_.address, (p, a) => p.copy(address = a))

    // proposed
    class PimpedLens[A](l: Lens[A, Person]) {
      val name: Lens[A, String] = l andThen Person.name
      val address: Lens[A, Address] = l andThen Person.address
    }

    implicit def pimpLens[A](l: Lens[A, Person]) = new PimpedLens(l)
  }

  object Address {
    // Generated
    val street: Lens[Address, String] = Lens(_.street, (p, s) => p.copy(street = s))

    // proposed
    class PimpedLens[A](l: Lens[A, Address]) {
      val street: Lens[A, String] = l andThen Address.street
    }

    implicit def pimpLens[A](l: Lens[A, Address]) = new PimpedLens(l)
  }

  val p = Person("Brent", Address("Main St"))

  Person.address.street.set(p, "Lower Main St") 
}