I find Haskell quite complicated, involving abstract concepts you would likely not consciously encounter in other languages (lenses, monad transformers, free monads, etc).
Lenses and monad transformers are libraries, not part of the language. It doesn't look like the book uses them, so you don't need to understand them in order to follow it:
I find Haskell quite complicated, involving abstract concepts you would likely not consciously encounter in other languages (lenses, monad transformers, free monads, etc).