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)

Id Monad

The same way Option encodes optionality, the Id represents nothing special. It wraps a value but does nothing with it. Why would we need something that's not a thing? The Id is kind of a meta-lifting, which can represent anything as an effect without changing it. How can this be done? Well, first of all, we have to say to the compiler that an Id[A] is the same thing as an A. This is easily done with a type alias:

type Id[A] = A

This type definition will dictate the details of the monad's implementation:

implicit val idMonad = new Monad[Id] {
override def unit[A](a: => A): Id[A] = a
override def flatMap[A, B](a: Id[A])(f: A => Id[B]): Id[B] = f(a)

Obviously, unit(a) is just a, and by having the type alias we just defined, we're making the compiler believe that it is not of type A, but an Id[A]. Similarly, with the flatMap, we can't do anything...