Book Image

Learn Scala Programming

By : Slava Schmidt
Book Image

Learn Scala Programming

By: Slava Schmidt

Overview of this book

The second version of Scala has undergone multiple changes to support features and library implementations. Scala 2.13, with its main focus on modularizing the standard library and simplifying collections, brings with it a host of updates. Learn Scala Programming addresses both technical and architectural changes to the redesigned standard library and collections, along with covering in-depth type systems and first-level support for functions. You will discover how to leverage implicits as a primary mechanism for building type classes and look at different ways to test Scala code. You will also learn about abstract building blocks used in functional programming, giving you sufficient understanding to pick and use any existing functional programming library out there. In the concluding chapters, you will explore reactive programming by covering the Akka framework and reactive streams. By the end of this book, you will have built microservices and learned to implement them with the Scala and Lagom framework.
Table of Contents (19 chapters)


The Traversable functor is similar to Reducible and Foldable, which we talked about in the previous chapter. The difference is that methods defined on Traversable preserve the underlying structure while going over it, as opposed to the other abstractions which collapse it into the single result. The Traversable defines two methods:

import scala.{ Traversable => _ }

trait Traversable[F[_]] extends Functor[F] {
def sequence[A,G[_]: Applicative](a: F[G[A]]): G[F[A]]
def traverse[A,B,G[_]: Applicative](a: F[A])(f: A => G[B]): G[F[B]]

Unfortunately, Scala has a deprecated Traversable definition left over from previous versions, so we are getting rid of it by using import renaming. Our Traversable defines the sequence and traverse methods, which loosely correspond to the reduce and fold methods defined on monoids. Starting with the sequence method, we can see that...