Effective Haskell

Chapter 4Creating New Types

In the last chapter, you learned the basics of how Haskell’s type system works, and you wrote some programs that made use of some of the common predefined types available in the standard library. Those fundamentals are an important building block to making effective use of Haskell’s type system, but the real power comes in creating your own types that let you precisely describe the structure and behavior of the data in your application. In this chapter, you’ll learn how to create your own types that accurately represent the structure of your data. Later, here, you’ll learn to go a step further and describe the behavior of your types as well.