Effective Haskell

Chapter 13Building Applications with Many Effects

Throughout this book you’ve learned several different ways to build up monadic computations that have their own particular properties, from Maybe computations that might not return a value and Either values that could succeed or have an error, to IO actions that might have any number of externally visible side effects like printing messages to the screen or updating an IORef. As you saw in the last chapter, many of the programs that we want to build involve several different types of effects that can be combined to build more sophisticated applications. Until now, when we’ve encountered a problem that required a novel combination of effects, we’ve built a new solution from scratch. Building up ...