Preface

You will need a working knowledge of Haskell, which is not covered in this book. For that, a good place to start is an introductory book such as Real World Haskell (O’Reilly), Programming in Haskell (Cambridge University Press), Learn You a Haskell for Great Good! (No Starch Press), or Haskell: The Craft of Functional Programming (Addison-Wesley).

The main goal of the book is to get you programming competently with Parallel and Concurrent Haskell. However, as you probably know by now, learning about programming is not something you can do by reading a book alone. This is why the book is deliberately practical: There are lots of examples that you can run, play with, and extend. Some of the chapters have suggestions for exercises you can try out to get familiar with the topics covered in that chapter, and I strongly recommend that you either try a few of these, or code up some of your own ideas.

As we explore the topics in the book, I won’t shy away from pointing out pitfalls and parts of the system that aren’t perfect. Haskell has been evolving for over 20 years but is moving faster today than at any point in the past. So we’ll encounter inconsistencies and parts that are less polished than others. Some of the topics covered by the book are very recent developments: Chapters 4, 5, 6, and pass:[14 cover frameworks that were developed in the last few years.

The book consists of two mostly independent parts: Part I and Part II. You should feel free to start with either part, or to flip between them (i.e., read them concurrently!). There is only one dependency between the two parts: Chapter 13 will make more sense if you have read Part I first, and in particular before reading “The ParIO monad”, you should have read Chapter 4.

While the two parts are mostly independent from each other, the chapters should be read sequentially within each part. This isn’t a reference book; it contains running examples and themes that are developed across multiple chapters.

The following typographical conventions are used in this book:

Code samples look like this:

timetable1.hs

search :: ( partial -> Maybe solution )   -- 
       -> ( partial -> [ partial ] )
       -> partial
       -> [solution]

The heading gives the filename of the source file containing the code snippet, which may be found in the sample code; see “Sample Code” for how to obtain the sample code. When there are multiple snippets quoted from the same file, usually only the first will have the filename heading.

Commands that you type into the shell look like this:

$ ./logger
hello
bye
logger: stop

The $ character is the prompt, the command follows it, and the rest of the lines are the output generated by the command.

GHCi sessions look like this:

> extent arr
(Z :. 3) :. 5
> rank (extent arr)
2
> size (extent arr)
15

I often set GHCi’s prompt to the character > followed by a space, because GHCi’s default prompt gets overly long when several modules are imported. You can do the same using this command in GHCi:

Prelude> :set prompt "> "
>

The sample code that accompanies the book is available online; see “Sample Code” for details on how to get it and build it. For information on your rights to use, modify, and redistribute the sample code, see the file LICENSE in the sample code distribution.

Technology professionals, software developers, web designers, and business and creative professionals use Safari Books Online as their primary resource for research, problem solving, learning, and certification training.

Safari Books Online offers a range of product mixes and pricing programs for organizations, government agencies, and individuals. Subscribers have access to thousands of books, training videos, and prepublication manuscripts in one fully searchable database from publishers like O’Reilly Media, Prentice Hall Professional, Addison-Wesley Professional, Microsoft Press, Sams, Que, Peachpit Press, Focal Press, Cisco Press, John Wiley & Sons, Syngress, Morgan Kaufmann, IBM Redbooks, Packt, Adobe Press, FT Press, Apress, Manning, New Riders, McGraw-Hill, Jones & Bartlett, Course Technology, and dozens more. For more information about Safari Books Online, please visit us online.

Please address comments and questions concerning this book to the publisher:

We have a web page for this book, where we list errata, examples, and any additional information. You can access this page at http://oreil.ly/parallel-concurrent-prog-haskell.

To comment or ask technical questions about this book, send email to <bookquestions@oreilly.com>.

For more information about our books, courses, conferences, and news, see our website at http://www.oreilly.com.

Find us on Facebook: http://facebook.com/oreilly

Follow us on Twitter: http://twitter.com/oreillymedia

Watch us on YouTube: http://www.youtube.com/oreillymedia

For several months I have had a head full of Parallel and Concurrent Haskell without much room for anything else, so firstly and most importantly I would like to thank my wife for her encouragement, patience, and above all, cake, during this project.

Secondly, all of this work owes a lot to Simon Peyton Jones, who has led the GHC project since its inception and has always been my richest source of inspiration. Simon’s relentless enthusiasm and technical insight have been a constant driving force behind GHC.

Thanks to Mary Sheeran and Andres Löh (among others), who persuaded me to turn my tutorial notes into this book, and thanks to the organizers of the CEFP and CEA/EDF/INRIA summer schools for inviting me to give the courses that provided the impetus to get started, and to the students who attended those courses for being my guinea pigs.

Many thanks to my editor, Andy Oram, and the other folks at O’Reilly who helped this book become a reality.

The following people have helped with the book in some way, either by reviewing early drafts, sending me suggestions, commenting on the online chapters, writing some code that I borrowed (with attribution, I hope), writing a paper or blog post from which I took ideas, or something else (if I’ve forgotten you, I’m sorry): Joey Adams, Lennart Augustsson, Tuncer Ayaz, Jost Berthold, Manuel Chakravarty, Duncan Coutts, Andrew Cowie, Iavor Diatchki, Chris Dornan, Sigbjorn Finne, Kevin Hammonad, Tim Harris, John Hughes, Mikolaj Konarski, Erik Kow, Chris Kuklewicz, John Launchbury, Roman Leshchinskiy, Ben Lippmeier, Andres Löh, Hans-Wolfgang Loidl, Ian Lynagh, Trevor L. McDonell, Takayuki Muranushi, Ryan Newton, Mary Sheeran, Wren ng Thornton, Bryan O’Sullivan, Ross Paterson, Thomas Schilling, Michael Snoyman, Simon Thomson, Johan Tibell, Phil Trinder, Bas Van Dijk, Phil Wadler, Daniel Winograd-Cort, Nicolas Wu, and Edward Yang.

Finally, thanks to the Haskell community for being one of the most friendly, inclusive, helpful, and stimulating online open source communities I’ve come across. We have a lot to be proud of, folks; keep it up.