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Herausgeber: Packt Publishing
Kategorie: Wissenschaft und neue Technologien
Sprache: Englisch

Beschreibung

Save time and build fast, functional, and concurrent application using Haskell

About This Book

Comprehensive guide for establishing a strong foundation in Haskell and developing pragmatic code
Create a full fledged web application using Haskell
Work with Lens, Haskell Extensions, and write code for concurrent and distributed applications

Who This Book Is For

This book is targeted at readers who wish to learn the Haskell language. If you are a beginner, Haskell Cookbook will get you started. If you are experienced, it will expand your knowledge base. A basic knowledge of programming will be helpful.

What You Will Learn

Use functional data structures and algorithms to solve problems
Understand the intricacies of the type system
Create a simple parser for integer expressions with additions
Build high-performance web services with Haskell
Master mechanisms for concurrency and parallelism in Haskell
Perform parsing and handle scarce resources such as filesystem handles
Organize your programs by creating your own types and type classes

In Detail

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.

Style and approach

The book follows a recipe-based approach. Each recipe addresses specific problems and issues. The recipes provide discussions and insights to explain these problems.

Details

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Seitenzahl: 393

Veröffentlichungsjahr: 2017

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Leseprobe

Haskell Cookbook

Build functional applications using Monads, Applicatives, and Functors

Yogesh Sajanikar

BIRMINGHAM - MUMBAI

Haskell Cookbook

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: September 2017

Production reference: 1210917

Published by Packt Publishing Ltd.

Livery Place

35 Livery Street

Birmingham

B3 2PB, UK.

ISBN 978-1-78646-135-3

www.packtpub.com

Credits

Author

Yogesh Sajanikar

Copy Editor

Karuna Narayanan

Reviewer

Fabian Linzberger

Project Coordinator

Prajakta Naik

Commissioning Editor

Aaron Lazar

Proofreader

Safis Editing

Acquisition Editor

Karan Sadawana

Indexer

Francy Puthiry

ContentDevelopmentEditor

Siddhi Chavan

Graphics

Abhinash Sahu

Technical Editor

Supriya Thabe

Production Coordinator

Nilesh Mohite

About the Author

Yogesh Sajanikar has received his bachelor's degree in Mechanical Engineering from Shivaji University, India, along with a gold medal and a master's degree in Production Engineering from the Indian Institute of Technology, Bombay, India.

Yogesh has an experience of more than 20 years, and he has extensively worked with Product Lifecycle Management (PLM) and Computer Aided Design (CAD) software development firms, and architected solutions for domains such as Construction and Shipping Domain.

Having hooked on to functional programming, he moved into the Finance domain and worked as an enterprise architect; he has also worked with Scala/F# and Haskell. Currently, he is working as a CTO for a startup. He has also started local Haskell meetups and has been an active participant in meetups and functional conferences.

Yogesh believes in the open source movement, and believes in giving back to the open source community.

I would like to sincerely thank my wife, Rashmi, for her constant encouragement and sacrifice; Atharva, my son, who has now decided to learn Haskell at an early age. I would like to take a moment to thank my mom, Geeta, and my late dad, Mukund, for enabling me in my life’s journey.

Last, but nonetheless, I would sincerely thank my friends and colleagues at work. In the end, all the thanks to the wonderful staff at Packt, especially Siddhi and Supriya, who worked really hard to bring this book to reality. Their perseverance and pursuance really helped me complete the book despite the delays on my side.

About the Reviewer

Fabian Linzberger is a functional programming enthusiast and practitioner. He discovered Haskell in 2010 and it has been his favorite programming language ever since. You can find some of his code (some of it in Haskell) on GitHub (https://github.com/lefant/) or visit his personal homepage and check out his blog (https://e.lefant.net/).

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Preface

What this book covers

What you need for this book

Who this book is for

Sections

Getting ready

How to do it…

How it works…

There's more…

Preface

Functional programming has been gaining lot of momentum recently. We are seeing different paradigms of functional programming creeping into imperative languages such as C++, C#, and Python. There are languages such as Scala that try to offer best of both worlds, that is, object-oriented programming and functional programming.

As Haskell is a pure and non-strict language, and strictly separates pureness from effect-full computations, it really stands out among these languages. Its strong theoretical basis, such as an elaborate type system, combined with concise and expressive syntax, gives Haskell a unique flavor. It really helps in programming declaratively by specifying what rather than how! In this book, we will focus on practical aspects of the language.Haskell Cookbook is meant for programmers who have a programming background. Most of the readers should be acquainted with an imperative language, such as Java/Python or C++.

This cookbook can be logically divided into two parts, the first five chapters serve as building blocks for programming in Haskell. These chapters cover syntactical and semantic details of the language by describing how to use and define functions and data types. In these chapters, we also cover type classes and the Functor, Applicative, and Monads concepts. The last seven chapters will introduce you to the practical aspects of usage of Haskell and its rich set of libraries. These chapters will take you through containers in Haskell and backend development (developing with database) to frontend development (web framework). The last three chapters focus on advanced concepts, such as doing parallel and distributed programming in Haskell.

Each recipe is self-sufficient, and, wherever possible, the recipe will try to build a concept (such as Monad) from scratch, before moving on to a recipe that will use the concept from the existing library. This is especially true in the first five chapters. Use this book to dive into Haskell and Functional Programming in general. Start building small toy programs by using recipes, and move on to bigger programs to create your own web application or a distributed system. Even if you are not planning to use Haskell in your day-to-day work, I can assure you that it will change the way you look at programming, even when programming with other languages.

This book is not possible without encouragements from my family and the constant pursuance and perseverance of the staff at Packt. These people believed in me even when I was delayed or transgressed.

What this book covers

Chapter 1, Foundations of Haskell, introduces you to Haskell and helps you setup the environment for Haskell using the stack as a tool. In this chapter, you will write your first Haskell program, and then analyze its parts.

Chapter 2, Getting Functional, warms you up to Haskell by introducing recursion, maps, filters, and folds. It ends up by implementing a prime sieve.

Chapter 3, Defining Data, explores the rich data types that Haskell provides. You will be exposed to product and sum types. This chapter further introduces standard type classes in Haskell.

Chapter 4, Working with Functors, Applicatives, and Monads, dives deeper into Haskell by exploring the rich type classes and their instances. The recipes in this chapter allow the reader to build their own monad, and introduces IO monad.

Chapter 5, More about Monads, builds on the previous chapter by further creating and using monad transformers, and finally building a parser with Attoparsec.

Chapter 6, Working with Common Containers and Strings, looks at common containers and introduces Foldable and Traversals. In this chapter, you will also cook your own container and test it using Quickcheck. This chapter also looks at an alternate representation of String, that is, Text and ByteString.

Chapter 7, Working with Relational and NoSQL Databases, uses the Haskell based model declaration template and queries using persistent library. We will also use redis to work with NoSQL databases.

Chapter 8, Working with HTML and Templates, works with the Heist template framework along with the Blaze HTML library to create composable HTML documents.

Chapter 9, Working with Snap Framework, explores various web application development aspects, such as routing, templating, authentication, and sessions using the Snap Framework.

Chapter 10, Working with Advanced Haskell, introduces you to advanced concepts such as Existentially Quantified Type, Rank-N-Type, type family, and GADT.

Chapter 11, Working with Lens and Prism, explores the lens library to look at the concept of Lens and Prism. This chapter explains the concept of lens by building one itself. The rest of the chapter explains rich features of the Lens library.

Chapter 12, Concurrent and Distributed Programming in Haskell, introduces the building blocks of concurrent programming, such as IORef, MVar, and STM. The later part introduces Cloud Haskell to create distributed applications.

What you need for this book

You will need a fairly recent operating system, such as Windows, Linux, or Mac OS.

You should set up the stack tool from

https://www.haskellstack.org/

. Use the Stack setup to download GHC (Haskell Compiler) on your machine. Stack is an extremely useful tool to work with different versions of GHC and packages.

You will need a good editor. Vi and Emacs have very good support for Haskell. Eclipse and Sublime also have support for Haskell.

Who this book is for

Sections

In this book, you will find several headings that appear frequently (Getting ready, How to do it, How it works, There's more, and See also).

To give clear instructions on how to complete a recipe, we use these sections as follows:

Getting ready

This section tells you what to expect in the recipe, and describes how to set up any software or any preliminary settings required for the recipe.

How to do it…

This section contains the steps required to follow the recipe.

How it works…

This section usually consists of a detailed explanation of what happened in the previous section.

There's more…

This section consists of additional information about the recipe in order to make the reader more knowledgeable about the recipe.

Reader feedback

Feedback from our readers is always welcome. Let us know what you think about this book--what you liked or disliked. Reader feedback is important for us as it helps us develop titles that you will really get the most out of.

To send us general feedback, simply e-mail [email protected], and mention the book's title in the subject of your message.

If there is a topic that you have expertise in and you are interested in either writing or contributing to a book, see our author guide at www.packtpub.com/authors.

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Now that you are the proud owner of a Packt book, we have a number of things to help you to get the most from your purchase.

Downloading the example code

You can download the example code files for this book from your account at http://www.packtpub.com. If you purchased this book elsewhere, you can visit http://www.packtpub.com/support and register to have the files e-mailed directly to you.

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The code bundle for the book is also hosted on GitHub at https://github.com/PacktPublishing/HaskellCookbook. We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out!

Errata

Although we have taken every care to ensure the accuracy of our content, mistakes do happen. If you find a mistake in one of our books--maybe a mistake in the text or the code--we would be grateful if you could report this to us. By doing so, you can save other readers from frustration and help us improve subsequent versions of this book. If you find any errata, please report them by visiting http://www.packtpub.com/submit-errata, selecting your book, clicking on the Errata Submission Form link, and entering the details of your errata. Once your errata are verified, your submission will be accepted and the errata will be uploaded to our website or added to any list of existing errata under the Errata section of that title.

To view the previously submitted errata, go to https://www.packtpub.com/books/content/support and enter the name of the book in the search field. The required information will appear under the Errata section.

Piracy

Piracy of copyrighted material on the Internet is an ongoing problem across all media. At Packt, we take the protection of our copyright and licenses very seriously. If you come across any illegal copies of our works in any form on the Internet, please provide us with the location address or website name immediately so that we can pursue a remedy.

Please contact us at [email protected] with a link to the suspected pirated material.

We appreciate your help in protecting our authors and our ability to bring you valuable content.

Questions

If you have a problem with any aspect of this book, you can contact us at [email protected], and we will do our best to address the problem.

Foundations of Haskell

In this chapter, we will cover the following recipes:

Getting started with Haskell

Working with data types

Working with pure functions and user-defined data types

Working with list functions

Getting started with Haskell

In this recipe, we will work with Glasgow Haskell Compiler (GHC) and its interpreter GHCi. Then, we will write our first Haskell program and run it in the interpreter.

We will use GHC throughout the book. GHC (https://www.haskell.org/ghc/) is the most widely used Haskell compiler. GHC supports Haskell 2010 language specifications (https://wiki.haskell.org/Definition). The current book is based on Haskell 2010 specifications. GHC supports an extensive range of language extensions.

How it works…

This recipe demonstrated the usage of Stack to create a new project, build it, set up the corresponding GHC version, build the project, and run it. The recipe also demonstrated the use of the Haskell command prompt, aka GHCi, to load and edit the file. GHCi also allows us to run the program in the command prompt.

The recipe also shows the familiar Hello World! program and how to write it. The program can be interpreted in the following way.

There's more…

If you visit the Stack website at https://www.stackage.org/, you will notice that Stack publishes nightly packages and Long Term Support (LTS) packages. While creating a new project, Stack downloads the latest LTS package list. It is also possible to provide the name of the LTS package explicitly by providing stack new –resolver lts-9.2.

In the project directory, you will notice two files:

<project>.yaml

<project>.cabal

The YAML file is created by Stack to specify various things, including LTS version, external packages, and so on. The .cabal file is the main project file for the Haskell package. The cabal is the tool that Stack uses internally to build, package, and so on. However, there are several advantages of using Stack as Stack also supports pre-built packages and manages cabal well. Furthermore, Stack also supports the Docker environment.

Working with data types

In this recipe, we will work with basic data types in Haskell. We will also define our own data types.

How it works...

We have seen four basic types Int, Double, Char, and Float. More information about these types is given in the following table:

Type

Description

Remarks

Int

Fixed precision integer type

Range [-9223372036854775808 to

9223372036854775807] for 64-bit Int.

Float

Single precision (

-bit) floating point number

Double

Double precision (

-bit) floating point number

Char

Character

Bool

Boolean values

True

False

Note that all types start with a capital letter.

In previous sections of this recipe, when we ran the command :info Bool, at GHCi prompt, Haskell also showed various instances of information. It shows more about the behavior of the type. For example, instance Eq Bool means that the type Bool is an instance of some type class Eq. In Haskell, type class should be read as a type that is associated with some behavior (or function). Here, the Eq type class is used in Haskell for showing equality.

There's more…

You can get more information about type classes by exploring :info Eq. GHCi will tell you which types have instances of the Eq type class. GHCi will also tell you which are the methods defined for Eq.

Working with pure functions and user-defined data types

In this recipe, we will work with pure functions and define simple user-defined data types. We will represent a quadratic equation and its solution using user-defined data types. We will then define pure functions to find a solution to the quadratic equation.

Getting ready

Create a new project

quadratic

using the following command:

stack new quadratic

Change into the project folder.

Delete

src/Lib.hs

and create a new file

src/Quadratic.hs

to represent the quadratic equation and its solution.

Open the

quadratic.cabal

file, and in the section library, replace

Lib

Quadratic

in the tag

exposed-modules

library

hs-source-dirs: src

exposed-modules: Quadratic

build-depends: base >= 4.7 && < 5

default-language: Haskell2010

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Haskell Cookbook E-Book

Yogesh Sajanikar

About This Book

Who This Book Is For

What You Will Learn

In Detail

Style and approach

Haskell Cookbook

Credits

About the Author

About the Reviewer

www.PacktPub.com

Why subscribe?

Customer Feedback

Table of Contents

Preface

What this book covers

What you need for this book

Who this book is for

Sections

Getting ready

How to do it…

How it works…

There's more…

See also

Reader feedback

Customer support

Downloading the example code

Errata

Piracy

Questions

Foundations of Haskell

Getting started with Haskell

How it works…

There's more…

Working with data types

How it works...

There's more…

Working with pure functions and user-defined data types

Getting ready