Michael Snoyman - Developing Web Apps with Haskell and Yesod: Safety-Driven Web Development

by Michael Snoyman

Copyright 2015 Michael Snoyman. All rights reserved.

Printed in the United States of America.

Published by OReilly Media, Inc. , 1005 Gravenstein Highway North, Sebastopol, CA 95472.

OReilly books may be purchased for educational, business, or sales promotional use. Online editions are also available for most titles (http://safaribooksonline.com). For more information, contact our corporate/institutional sales department: 800-998-9938 or corporate@oreilly.com .

• Editors: Simon St. Laurent and Allyson MacDonald
• Production Editor: Nicole Shelby
• Copyeditor: Jasmine Kwityn
• Proofreader: Rachel Head
• Indexer: Ellen Troutman
• Interior Designer: David Futato
• Cover Designer: Ellie Volckhausen
• Illustrator: Rebecca Demarest

• February 2015: Second Edition

See http://oreilly.com/catalog/errata.csp?isbn=9781491915592 for release details.

The OReilly logo is a registered trademark of OReilly Media, Inc. Developing Web Apps with Haskell and Yesod, Second Edition, the cover image, and related trade dress are trademarks of OReilly Media, Inc.

While the publisher and the author have used good faith efforts to ensure that the information and instructions contained in this work are accurate, the publisher and the author disclaim all responsibility for errors or omissions, including without limitation responsibility for damages resulting from the use of or reliance on this work. Use of the information and instructions contained in this work is at your own risk. If any code samples or other technology this work contains or describes is subject to open source licenses or the intellectual property rights of others, it is your responsibility to ensure that your use thereof complies with such licenses and/or rights.

978-1-491-91559-2

[LSI]

Its fair to say that dynamic languages currently dominate the web development scene. Ruby, Python, and PHP are common choices for quickly creating a powerful web application. They provide a much faster and more comfortable development setting than standard static languages in the C family, like Java.

But some of us are looking for a bit more in our development toolbox. We want a language that gives us guarantees that our code is doing what it should. Instead of writing up a unit test to cover every bit of functionality in our application, wouldnt it be wonderful if the compiler could automatically ensure that our code is correct? And as an added bonus, wouldnt it be nice if our code ran quickly too?

These are the goals of Yesod. Yesod is a web framework bringing the strengths of the Haskell programming language to the web development world. Yesod not only uses a pure language to interact with an impure world, but allows safe interactions with the outside world by automatically sanitizing incoming and outgoing data. It helps us avoid basic mistakes such as mixing up integers and strings, and even allows us to statically prevent many cases of security holes like cross-site scripting (XSS) attacks.