The Typeclassopedia, by all accounts, has turned out to be a popular and useful resource for Haskell programmers. I’ve been thinking for a while about putting out a revised and expanded second edition, and it’s finally time. Planned changes include:

making suggested exercises stand out typographically and adding many more;

updating information about various standard packages (mtl, transformers, etc.) to match the current state of affairs;

switching away from Pointed as a stepping stone to Applicative in favor of a more semigroupoid-based approach;

expanding the sections on comonads and arrows, which were a bit rushed in the first edition;

many other small additions, clarifications, and corrections.

However, the first edition was immeasurably improved by suggestions and contributions from many readers, and I hope the same will be true for the second. So, what would you like to see in the second edition? Some prompts to help you think of ways to contribute:

Is there a section you find confusing? Do you have a suggestion to improve its clarity?

Do you have a suggestion for a good exercise?

Do you know of an error, whether technical or typographical?

Do you know of a good resource that could be added to the bibliography — an explanation, example, original/historical source, relevant humor, … ?

Are you able and willing to contribute some text explaining some aspect of a more advanced type class (Category, Comonad, Arrow, …) in more depth, or more intuitively, than the existing text?

To contribute, you can send me email (byorgey at cis dot upenn dot edu). I’ll also be keeping this darcs repository up to date, so you’re welcome to send me darcs patches as well.

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