Partial lenses (Scalaz 7)

gistfile1.scala

case class Person(pants: Option[Pants])
case class Pants(pocket: Option[Pocket])
case class Pocket(cash: Option[Cash])
case class Cash(value: String)

val pants: Person @-@ Option[Pants] =
  lensG(_.pants, p => ps => p.copy(pants = ps))
val pocket: Pants @-@ Option[Pocket] =
  lensG(_.pocket, ps => p => ps.copy(pocket = p))
val cash: Pocket @-@ Option[Cash] =
  lensG(_.cash, p => c => p.copy(cash = c))
val value: Cash @-@ String =
  lensG(_.value, c => v => c.copy(value = v))

val someCashValue: Person @-? String =
  ~pants <=< somePLens <=<
  ~pocket <=< somePLens <=<
  ~cash <=< somePLens <=<
  ~value

val ben = Person(Some(Pants(Some(Pocket(Some(Cash("zilch")))))))

someCashValue.mod(_ + ", zero, nada", ben)
// Person(Some(Pants(Some(Pocket(Some(Cash(zilch, zero, nada)))))))