Developing Web Apps with Haskell and Yesod, 2nd Edition

Chapter 2. Haskell

Haskell is a powerful, fast, type-safe, functional programming language. This book takes as an assumption that you are already familiar with most of the basics of Haskell. There are two wonderful books for learning Haskell, both of which are available for reading online:

• Learn You a Haskell for Great Good! by Miran Lipovača (No Starch Press)

• Real World Haskell by Bryan O’Sullivan, John Goerzen, and Donald Bruce Stewart (O’Reilly)

Additionally, there are a number of great articles on School of Haskell.

In order to use Yesod, you’re going to have to know at least the basics of Haskell. Additionally, Yesod uses some features of Haskell that aren’t covered in most introductory texts. While this book assumes the reader has a basic familiarity with Haskell, this chapter is intended to fill in the gaps.

If you are already fluent in Haskell, feel free to completely skip this chapter. Also, if you would prefer to start off by getting your feet wet with Yesod, you can always come back to this chapter later as a reference.

Terminology

Even for those familiar with Haskell as a language, there can occasionally be some confusion about terminology. Let’s establish some base terms that we can use throughout this book:

Data type

This is one of the core building blocks for a strongly typed language like Haskell. Some data types (e.g., Int) can be treated as primitive values, while other data types will build on top of these to create more complicated values. For example, ...