Scala Programming Projects

Usage examples

In the section cats.Apply about Apply, you saw that we can combine many values in an F context by using mapN. However, what if the values that we want to combine are in a collection instead of a tuple?

In that case, we can use the Traverse type class. Cats provide instances of this type class for many collection types, such as List, Vector, and SortedMap.

The following is a simplified definition of Traverse:

@typeclass trait Traverse[F[_]] extends Functor[F] with Foldable[F] with UnorderedTraverse[F] { self =>
  def traverse[G[_]: Applicative, A, B](fa: F[A])(f: A => G[B]):   G[F[B]]
  (...)
}

This signature means that I can call it with a collection, fa: F[A] (for instance, Vector[String]), and a function that takes A and returns ...