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

Pipes and filters

Unix and Linux shells approach problems with the use of the pipes and filters pattern. Here is how we could implement the inverted index in GNU awk, gawk:

  FS = "->"
  split($2, a, " ")
  for (x in a) {
    w = a[x]
    # print w
    iidx[w] = iidx[w] $1
  for(w in iidx) {
    print w " -> " iidx[w]

Here is an example of pipes and filters:

echo 'Carr -> And So To Murder
Carr -> The Arabian Nights Murder
Carr -> The Mad Hatter Mystery
Christie -> The Murder Of Roger Ackroyd
Christie -> The Sittaford Mystery
Carr -> The Plague Court Murders' | sed -E 's/The|Of|And|To|So//g' | gawk -f iidx.awk 

Note that we pipe in the input text to sed. Sed filters out uninteresting words and passes on the rest of the text to awk. Awk generates the inverted index using features such as field splitting and associative arrays (which are similar to hash maps).

Note that I can combine these tools in many ways. For example, I could implement...