Author here. I wanted to share that Effective Haskell is now out of beta and available as both a DRM-free eBook and available in print. Since I've finished writing the book, I've been working on putting up some extra content at
https://effective-haskell.com. The site is still quite a work in progress, but there are solutions to the exercises in the first half of the book so far, plus detailed descriptions of each exercise and chapter.