Book Image

Haskell Cookbook

Book Image

Haskell Cookbook

Overview of this book

Haskell is a purely functional language that has the great ability to develop large and difficult, but easily maintainable software. Haskell Cookbook provides recipes that start by illustrating the principles of functional programming in Haskell, and then gradually build up your expertise in creating industrial-strength programs to accomplish any goal. The book covers topics such as Functors, Applicatives, Monads, and Transformers. You will learn various ways to handle state in your application and explore advanced topics such as Generalized Algebraic Data Types, higher kind types, existential types, and type families. The book will discuss the association of lenses with type classes such as Functor, Foldable, and Traversable to help you manage deep data structures. With the help of the wide selection of examples in this book, you will be able to upgrade your Haskell programming skills and develop scalable software idiomatically.
Table of Contents (13 chapters)

Working with Foldable and Traversable

In this recipe, we will work with two type classes, Traversable, and Foldable. Both these classes are the generalization of the functions that we have seen when working with Lists. Traversable, as the name suggests, allows us to browse a data structure to traverse from left to right. Similarly, the Foldable type class allows us to fold the elements of a data type.

In fact, in previous versions of GHC, traversals and folding were defined for lists. In recent versions, those functions are generalized to include Traversable and Foldable, making them applicable to a wide range of data structures.

We will also define Traversable and Foldable instances for a tree.

How to do it...

  1. Create a new...