As far as beginning Haskell books go, I think this is probably the best one out there. In the past I enjoyed reading the classic "Learn you A Haskell For Great Good" as my first foray into Haskell, but was disappointed in the lack of exercises. This book not only remedies that, but exceeds most other texts 10 fold (indeed there seems to be no limit at times, though this can definitely be helpful while trying to tackle what is generally agreed to be one of the toughest languages to learn). Having recently started my professional journey into Haskell-land, this book also does a pretty good job of filling in the cracks by covering some topics considered to be intermediate-level such as Monad Transformers. Though to get a true intermediate experience, I think you'd have to look into other books such as "Real World Haskell".
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