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)

Chapter 9

  1. Implement Monad[Try].
implicit val tryMonad = new Monad[Try] {
override def unit[A](a: => A): Try[A] = Success(a)

override def flatMap[A, B](a: Try[A])(f: A => Try[B]): Try[B] = a match {
case Success(value) => f(value)
case Failure(ex) => Failure(ex)
  1. Prove the right identity law for the State monad.

Let's start with the property definition we had in this chapter:

val rightIdentity = forAll { (a: A, f: A => M[B]) =>
M.flatMap(M.unit(a))(f) == f(a)

Let f(a) = a => State(s => (b, s2))

First, we substitute the definition of unit with the result of the call. Hence, M.flatMap(M.unit(a))(f) becomes M.flatMap(State(s => (a, s)))(f).

Next, we substitute M.flatMap with compose, which gives us State(s => (a, s)).compose(f).

Next, we'll use the lemma proved in this chapter to substitute the compose call with the definition...