Functional Programming in Scala

Part 4. Effects and I/O

Functional programming is a complete programming paradigm. All programs that we can imagine can be expressed functionally, including those that mutate data in place and interact with the external world by writing to files or reading from databases. In this part, we’ll apply what we covered in parts 1–3 of this book to show how FP can express these effectful programs.

We’ll begin in the next chapter by examining the most straightforward handling of external effects, using an I/O monad. This is a simplistic embedding of an imperative programming language into a functional language. The same general approach can be used for handling local effects and mutation, which we’ll introduce in chapter 14. Both of these chapters ...