Programming Scala, 3rd Edition

Chapter 7. Functional Programming in Scala

It is better to have 100 functions operate on 1 data structure than 10 functions on 10 data structures.

Alan J. Perlis

This chapter introduces functional programming (FP). Even if you have prior experience with FP in other languages, you should still skim the chapter for Scala-specific details. I’ll start with an explanation of the origin and value of FP and then discuss in depth the many ways functions can be used and manipulated in Scala. I’ll finish with a discussion of the power and flexibility of functional data structures and their composable operations. Chapter 18 discusses more advanced concepts in FP.

What Is Functional Programming?

Every decade or two, a major computing idea goes mainstream. The idea may have lurked in the background of academic computer science research or in obscure corners of industry, perhaps for decades. The transition to mainstream acceptance comes in response to a perceived problem for which the idea is well suited. Object-oriented programming (OOP), which was invented in the 1960s, went mainstream in the 1980s, arguably in response to the emergence of graphical user interfaces (GUIs), for which the OOP paradigm is a natural fit.

FP experienced a similar breakout over the last 15 years or so. FP is actually much older than OOP, going back to theoretical work in the 1930s! FP offers effective techniques for three major challenges that became pressing in the 2000s and remain pressing today:

• The need ...