I guess two questions here for myself and in general. Does your book require existing knowledge in Haskell? Haskell in general, would you recommend it as a first language or something for a beginner programmer?
Haskell in Depth is definitely not the first book in one's life to learn Haskell. I assume a reader already having a pretty solid background. Get Programming with Haskell by Will Kurt is much more suitable for creating such a background. Unfortunately, I never saw any educational material on Haskell that is usable for introducing programming per se without any prior knowledge in programming. This is definitely possible with a teacher, although it can be very hard to find one.
Yea, functional first is an interesting approach. I read about some places doing that with Racket and using the Dr. Racket IDE as a way to teach non-programmers how to code. MIT has it's scheme coursework too, but it's also not beginner material.