https://stackoverflow.com/questions/45180179/why-in-haskell-00-1
http://learnyouahaskell.com/input-and-output

https://gist.github.com/kirelagin/3886243

https://stackoverflow.com/questions/1153465/what-does-the-symbol-mean-in-reference-to-lists-in-haskell

http://www.cs.utoronto.ca/~trebla/CSCC24-2020-Winter/02-haskell-types-1.html