This version is open for comments on a paragraph basis. Click on the link after a paragraph to comment on it. The comment will appear once the administrators validate it.

The goal of the comment is not only to find errata, but to build collaboratively a better, more useful text for the whole community. New developments, issues that need clarification or expansion, and questions, both specific and open-ended, are very welcome.

The authors will do their best to review timely, and give useful feedback when appropriate.

We would like to thank Bryan O’Sullivan, Don Stewart, and John Goerzen, authors of the book Real World Haskell, for inspiring us and letting us use their software, and Carles Balsells and Clint Dilks for adapting it and setting up the server.