Effective Haskell

Reading Type Errors

One of the most beneficial aspects of Haskell’s type system is in its ability to generate type errors. Errors might sound like a bad thing, but Haskell’s type errors help you refactor your code more quickly and find problems with your program early on in the development cycle before your code gets to users. In this section, you’ll see some simple type errors and learn how to read the compiler’s output and use it to fix errors in your program. Haskell type errors can grow quite long and become complex to read as you introduce more features of the type system into your program. For now, we’ll start out with some minimal examples, and throughout this book we’ll return to type errors that might come up as you’re using new features ...