Book Image

Scala Functional Programming Patterns

By : Atul S. Khot
Book Image

Scala Functional Programming Patterns

By: Atul S. Khot

Overview of this book

Scala is used to construct elegant class hierarchies for maximum code reuse and extensibility and to implement their behavior using higher-order functions. Its functional programming (FP) features are a boon to help you design “easy to reason about” systems to control the growing software complexities. Knowing how and where to apply the many Scala techniques is challenging. Looking at Scala best practices in the context of what you already know helps you grasp these concepts quickly, and helps you see where and why to use them. This book begins with the rationale behind patterns to help you understand where and why each pattern is applied. You will discover what tail recursion brings to your table and will get an understanding of how to create solutions without mutations. We then explain the concept of memorization and infinite sequences for on-demand computation. Further, the book takes you through Scala’s stackable traits and dependency injection, a popular technique to produce loosely-coupled software systems. You will also explore how to currying favors to your code and how to simplify it by de-construction via pattern matching. We also show you how to do pipeline transformations using higher order functions such as the pipes and filters pattern. Then we guide you through the increasing importance of concurrent programming and the pitfalls of traditional code concurrency. Lastly, the book takes a paradigm shift to show you the different techniques that functional programming brings to your plate. This book is an invaluable source to help you understand and perform functional programming and solve common programming problems using Scala’s programming patterns.
Table of Contents (19 chapters)
Scala Functional Programming Patterns
About the Author
About the Reviewers

Tail recursion to the rescue

There is a technique, an optimization really, that helps us get out of the logjam. However, we need to tweak the code a bit for this. We will make the recursive call as the last and only call. This means that there is no intermediate context to remember. This last and only call is called the tail call. Code in this tail call form is amenable to TCO. Scala generates code that, behind the scenes, uses a loop—the generated code does not use any stack frames:


def count(list: List[Int]): Int = {
  @tailrec   // 1
  def countIt(l: List[Int], acc: Int): Int = l match 
  case Nil => acc // 2
    case head :: tail => countIt(tail, acc+1) // 3 
  countIt(list, 0)

The changes are like this:

We have a nested workhorse method that is doing all the hard work. The count method calls the countIt nested recursive method, with the list it got in the argument, and an accumulator. The earlier intermediate context is now expressed...