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.

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Table of Contents (13 chapters)
Preface
Preface
What this book covers
What you need for this book
Who this book is for
Sections
Conventions
Reader feedback
Customer support
Free Chapter
1
Foundations of Haskell
Foundations of Haskell
Introduction
Getting started with Haskell
Working with data types
Working with pure functions and user-defined data types
Working with list functions
2
Getting Functional
Getting Functional
Introduction
Working with recursive functions
Reversing a list - Recursive worker function pattern
Creating maps and filters
Working with laziness and recursion
Working with folds
Sorting a list
Implementing merge sort
Implementing Eratosthenes Sieve
3
Defining Data
Defining Data
Introduction
Defining a product type
Defining a sum type
Defining a binary tree and traversing it
Defining data with functions
Using Maybe
Using Either
Working with type classes
Working with Monoid
4
Working with Functors, Applicatives, and Monads
Working with Functors, Applicatives, and Monads
Introduction
Working with Functors
Binary tree as Functor
Working with Applicatives
Binary tree as Applicative
Working with monad
List as monad
Working with IO monad
Writing INI parser
Errors and exception handling
5
More about Monads
More about Monads
Introduction
Writing a State Monad
Computing a fibonacci number with State Monad
Writing a State Monad transformer
Working with the Reader monad transformer
Working with the Writer monad transformer
Combining monad transformers
6
Working with Common Containers and Strings
Working with Common Containers and Strings
Introduction
Working with sets
Shopping cart as a set
Working with maps
Log analysis with map
Working with vector
Working with text and bytestring
Creating and testing a priority queue
Working with Foldable and Traversable
7
Working with Relational and NoSQL Databases
Working with Relational and NoSQL Databases
Introduction
Working with Persistent
Managing migrations
Creating custom data types
Using Esqueleto to do advanced SQL queries
Using hedis to work with redis (key-value, list and hash)
Using hashsets and sorted sets in redis to create a Trie
8
Working with HTML and Templates
Working with HTML and Templates
Introduction
Using blaze to create an HTML template
Using blaze to reverse engineer an HTML page
Use blaze-html with Bootstrap to create HTML template
Using heist as a template engine
Working with splice in Heist
9
Working with Snap Framework
Working with Snap Framework
Introduction
Getting started with Snap
Routing in Snap
Serving static contents in Snap
Form handling in Snap
Creating and composing snaplets
Session handling in Snap
Authentication in Snap
File upload with Snap
10
Working with Advanced Haskell
Working with Advanced Haskell
Introduction
Working with existentially quantified type
Working with Rank-N type
Working with type family
Working with GADTs
11
Working with Lens and Prism
Working with Lens and Prism
Introduction
Creating lenses
Working with lenses
Working with Traversal
Working with Iso
Working with Prism
Working with predefined lenses
12
Concurrent and Distributed Programming in Haskell
Concurrent and Distributed Programming in Haskell
Introduction
Working with IORef
Working with MVar
Working with STM
Working with strategies
Working with monad-par
Working with Cloud Haskell
Using Cloud Haskell to start master and slave nodes
Using closure to communicate between nodes

Creating maps and filters

In this recipe, we will continue working with recursive functions. In addition to recursion, we will introduce higher order functions. Higher order functions are functions that take other functions as an argument. Higher order functions introduce a layer of abstraction over other functions. If you see a certain pattern repeated over and over again, then you might have hit a situation that can be abstracted as a higher order function.

Though provided by default by Haskell's Prelude module, we will write our own version of two important higher order functions, map and filter.

Getting ready

Using stack, create a new project, map-filter, using the simple template. Change to the project folder and...

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