Hans-J. Schmid (16) [Avatar] Offline
As far as I could understand there are monad transformers used in this chapter behind the scenes. Is there some good background information about it?

Side notes: I like this chapter very much as it builds up section by section. It's very systematic, pedagogical and motivating as the whole book actually. It was also a good idea to outsource the Effects library as there is already a great tutorial on the internet.

Kind regards!
Edwin Brady (65) [Avatar] Offline
There's a monad transformer behind the scenes in the first State example, but I decided not to go into any depth on that because the next couple of chapters build on very different ideas - tracking state changes in types - where monad transformers don't work so well, in my experience at least.

This is a reasonable brief introduction, which includes the State transformer specifically: https://en.wikibooks.org/wiki/Haskell/Monad_transformers