Comment by johtela

If you want to learn how HM typechecking works by studying working (Haskell) code, I would recommend the papers below. The code in these papers is closer to how you would actually implement a type checker in practice.

[1]: https://www.microsoft.com/en-us/research/wp-content/uploads/...

[2]: https://web.cecs.pdx.edu/~mpj/thih/thih.pdf