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)

Monad transformers stacks

In the meantime, we'll entertain ourselves with the following ideas:

  • Monad transformers require an instance of a monad for the outer layer
  • A monad transformer itself has a monad
  • Will something bad happen if we use a monad transformer as an instance of a monad for another monad transformer?

Let's try it out. We've already implemented two monad transformers so let's bring them together. To start, we'll define the type of stack. It will be EitherT wrapped in OptionT. This will give us an unwrapped type of the following code:

Future[Either[String, Option[Fish]]]

This can be interpreted as an operation which takes time and might return an error in the case of nontechnical failure and needs to have an explanation (technical failures are denoted by failed Futures). An Option represents an operation which can return no result in a...