Another optics question: given:

data class Foo(x: Int)
data class Bar(y: String, foo: Foo)
data class AllTheBars(bars: List<Bar>)

is it possible get a focus (Lens or Optional) that is List<Bar> -> List<Foo>? What I'm really trying to do is come up with an Optional<AllTheBars, Foo> that focuses on a Foo that satisfies a particular predicate.