If the lens you're trying to compose with the map lens is a partial lens, you can just use compose
:
import scalaz._, Scalaz._, PLens._
def headFoo[A] = listHeadPLens[A] compose mapVPLens("foo")
And then:
scala> headFoo.get(Map("foo" -> List(42)))
res0: Option[Int] = Some(42)
scala> headFoo.get(Map("foo" -> Nil))
res1: Option[Nothing] = None
scala> headFoo.get(Map("bar" -> List(13)))
res2: Option[Int] = None
Note that this is Scalaz 7.
If the lens you want to compose isn't partial, you can make it so with ~
:
scala> def firstFoo[A, B] = ~Lens.firstLens[A, B] compose mapVPLens("foo")
firstFoo: [A, B]=> scalaz.PLensFamily[Map[String,(A, B)],Map[String,(A, B)],A,A]
scala> firstFoo.get(Map("foo" -> (42, 'a)))
res6: Option[Int] = Some(42)
There's also a .partial
method if you don't like the unary operator.