Parallel and Concurrent Programming in Haskell – online beta
chimera.labs.oreilly.com
chimera.labs.oreilly.com
[1] http://book.realworldhaskell.org/read/
[2] https://realworldocaml.org (also in beta)
EDIT: Found this http://chimera.labs.oreilly.com/about and also realised I was getting the toggle the wrong way around. "Comments on" means they're on, not 'click to turn them on'. Then you click on a block of text to bring up a comment box.