scalaz7

There's an example of a Scalaz map lens here : Dan Burton calls it containsKey , and it's inspired by the Edward Kmett talk. There is also something called mapVPLens in Scalaz 7 which is useful for modifying values in a map. My question is: if I have a lens for modifying type V , and a lens for a Map[K,V] , how can I compose them? I've been searching for a while for a good simple example, but there's still a dearth of examples in Scalaz. I'm interested in both Scalaz 6 and Scalaz 7 solutions. If the lens you're trying to compose with the map lens is a partial lens, you can just use compose :

I recently asked Map and reduce/fold over HList of scalaz.Validation and got a great answer as to how to transform a fixed sized tuple of Va[T] (which is an alias for scalaz.Validation[String, T] ) into a scalaz.ValidationNel[String, T] . I've since then been studying Shapeless and type level programming in general to try to come up with a solution that works on tuples of any size. This is what I'm starting out with: import scalaz._, Scalaz._, shapeless._, contrib.scalaz._, syntax.std.tuple._ type Va[A] = Validation[String, A] // only works on pairs of Va[_] def validate[Ret, In1, In2](params:

I am learning Scalaz and I have a project that already makes use of Scalaz7. Following this question I would like to use the function sequence[T](l: List[Option[T]]): Option[List[T]] (not that it is hard to write it myself). But the aforementioned question mentions Scalaz6. Where to find the sequence function in Scalaz7? It's defined in the scalaz.Traverse type class, where it looks like this: def sequence[G[_]:Applicative,A](fga: F[G[A]]): G[F[A]] = traversal[G].run[G[A], A](fga)(ga => ga) scalaz.syntax.TraverseOps provides a version that gets pimped onto List , since List has a Traverse