Pretty cool. They note that they are inspired by Go by Example [0] and Rust by Example [1], and this book seems stylistically similar to the community-driven Learn X in Y minutes site [2] which covers quick syntax/conceptual overviews for many other languages as well.

For the same target audience looking for free introductory coursework/exercises for Haskell, I'd recommend working through the Data61 Haskell course [3]. Brian McKenna has a nice Youtube series [4] covering it.

[0] https://gobyexample.com/

[1] https://doc.rust-lang.org/rust-by-example/index.html

[2] https://learnxinyminutes.com/

[3] https://github.com/system-f/fp-course#readme

[4] https://www.youtube.com/watch?v=NzIZzvbplSM