This is by Paul Hudak, one of the creators of Haskell. I took one of his classes that corresponds with this book. This is how I was introduced to Haskell.

Now I'm hooked on Haskell! The book is a truly excellent introduction to Haskell, and I suggest that anyone who is interested read it. The book goes into some interesting topics, including proofs by computation and induction, UIs and functional reactive programming, and arrows. And it elegantly explains some of the advantages of functional programming and the Haskell language.

Just note that this book is a work in progress; he is always updating and modifying the book as he teaches the corresponding classes.