Bryan O'Sullivan

Bryan O'Sullivan

Haskell hacker, distributed systems guy, writer, climber

San Francisco, California

Areas of Expertise:

  • Haskell
  • functional programming
  • distributed systems
  • revision control tools
  • Mercurial
  • consulting
  • speaking
  • programming
  • training
Bryan O'Sullivan is an Irish writer and developer who works with distributed systems, open source software, and programming languages. He wrote the award-winning O'Reilly title Real World Haskell. He has made significant contributions to the popular Mercurial revision control system, and to a number of other open source projects. He lives in San Francisco with his family. Whenever he can, he runs off to climb rocks.

Mercurial: The Definitive Guide Mercurial: The Definitive Guide
by Bryan O'Sullivan
June 2009
Print: $39.99
Ebook: $35.99

Real World Haskell Real World Haskell
by Bryan O'Sullivan, John Goerzen, Donald Bruce Stewart
November 2008
Print: $49.99
Ebook: $39.99

Bryan blogs at:

Win bigger statistical fights with a better jackknife

June 11 2014

(Summary: I’ve developed some algorithms for a statistical technique called the jackknife that run in O(n) time instead of O(n2).) In statistics, an estimation technique called “the jackknife” has been widely used for over half a century. It’s a mainstay…Read more › read more

A major upgrade to attoparsec: more speed, more power

May 31 2014

I’m pleased to introduce the third generation of my attoparsec parsing library. With a major change to its internals, it is both faster and more powerful than previous versions, while remaining backwards compatible. Comparing to C Let’s start with a…Read more › read more

Top Haskell packages seen through graph centrality beer goggles

May 18 2014

I threw together a little code tonight to calculate the Katz centrality of packages on Hackage. This is a measure that states that a package is important if an important package depends on it. The definition is recursive, as is…Read more › read more

Once more into the teach, dear friends

May 14 2014

Since the beginning of April, David Mazières and I have been back in the saddle teaching CS240H at Stanford again. If you’re tuning in recently, David and I both love systems programming, and we particularly get a kick out of…Read more › read more

Book review: Parallel and Concurrent Programming in Haskell

March 19 2014

It's time someone finally wrote a proper review of Simon Marlow's amazing book, Parallel and Concurrent Programming in Haskell. I am really not the right person to tackle this job objectively, because I have known Simon for 20 years and…Read more › read more

"I would recommend this book to anyone serious about learning Haskell or becoming better at functional programming. The authors do an excellent job of conveying why Haskell does things in certain ways, which leads to a better understanding of the language."
--Michael Dumont, Computer Science House

"Real World Haskell is the first Haskell introduction I've read that actually helped me understand why anyone would want to use the language. The focus on programming methods instead of just syntax made it much easier to think of practical applications for the language."
--Byron Clark,

"This is one of the best programming books that came out in recent years regardless of language."
--Gregory Knapen,

"I tried to learn Ocaml or Haskell before but was put off by the books available. This book is really different. It made me love Haskell."
--Emad S. Mohamed "Nawfal",

"For those who know a conventional language, this book will make you fall in love with Haskell."
--David Crawshaw,

"The book is a must-read for not only people who would specifically like to learn Haskell, but for any programmer who is open to new ways of thinking about computing. "
--Evgeny Kirpichov,

"The hardest problems in modern software lie in performance, modularity, reliability, and concurrency. With Real World Haskell, the authors do a great job of teaching how to tackle each of these problems with Haskell, a language that is generations ahead of today's mainstream."
--Tim Sweeney, founder of Epic Games, and designer of the Unreal game engine

"...this book will expand your mind. It will give you a new way of thinking about the whole enterprise of programming: when you have worked through these pages, you'll write better code in your current favourite language."
--Simon Peyton Jones, Microsoft Research, Haskell language architect and designer of the Glasgow Haskell Compiler

"This book is exactly what's needed--a deep and comprehensive guide, covering everything from fundamentals to a wealth of advanced topics, aimed at experienced programmers who want to harness Haskell's power to get the job done. I will be using it in my Advanced Programming classes from now on."
--Benjamin Pierce, Professor, Department of Computer and Information Science, University of Pennsylvania, author of Types and Programming Languages