Functional Programming in Scala

Chapter 4. Handling errors without exceptions

We noted briefly in chapter 1 that throwing exceptions is a side effect. If exceptions aren’t used in functional code, what is used instead? In this chapter, we’ll learn the basic principles for raising and handling errors functionally. The big idea is that we can represent failures and exceptions with ordinary values, and we can write higher-order functions that abstract out common patterns of error handling and recovery. The functional solution, of returning errors as values, is safer and retains referential transparency, and through the use of higher-order functions, we can preserve the primary benefit of exceptions—consolidation of error-handling logic. We’ll see how this works over the course ...