Partial Lens example

PartialLens.scala

object PartialLensExample extends App {

  import scalaz._
  import Lens._
  import PLens._


  case class Bar(blub: Option[String])
  case class Foo(bar: Option[Bar])

  // normal lenses for getting and setting values
  val fooBarL: Foo @> Option[Bar] = lensg(foo ⇒ bar ⇒ foo.copy(bar = bar), _.bar)
  val barBlubL: Bar @> Option[String] = lensg(bar ⇒ blub ⇒ bar.copy(blub = blub), _.blub)

  // compose the above as 'Partial Lenses', >=> is just an alias for 'andThen'
  val fooBarBlubL: Foo @?> String = fooBarL.partial >=> somePLens >=> barBlubL.partial >=> somePLens

  // try it
  val foo = Foo(Some(Bar(Some("Hi"))))

  println(fooBarBlubL.get(foo)) // Some(Hi)

  println(fooBarBlubL.set(foo, "Bye")) //Foo(Some(Bar(Some(Bye))))

  // this doesn't really work well
  val fooNone = Foo(None)
  println(fooBarBlubL.set(fooNone, "huh")) // None
}