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 10

  1. Why does the type of monad transformer reflect the type of the stack "upside-down"?

It is impossible to define a monad composition in general, only in a way specific to the internal effect of the stack. Because of this, the name of the effect is fixed in the name of the transformer and the outer effect becomes a type parameter.

  1. Why is it possible to reuse existing monads for the top layer of the stack?

The return type of the Kleisli arrow fits well with the type of the stack. For this reason, it is possible to produce the result of the proper type by utilizing the flatMap method of the outer monad.

  1. Why is it impossible to reuse existing monads for the bottom layer of the stack?

The argument type of the arrow expects a plain argument. Consequently, we need to extract the effect-free value from the context of internal effect. This is only possible in a...