Update: I just received my copy of the book, and at the bottom of page 4 the authors write: “It would be an interesting endeavour to port the code from Haskell

Update: I just received my copy of the book, and at the bottom of page 4 the authors write: “It would be an interesting endeavour to port the code from Haskell to a language with an even stronger type system, like Agda, Idris or Lean. The authors would welcome contributions in this direction.”