This is a short ebook written for Haskell programmers who wish to become comfortable with the concept of monad. It is formatted for reading on small or large screens. The author is a math Ph.D. with decades of experience teaching abstract concepts to beginners, including teenagers. "From Simple IO to Monad Transformers" could shave an hour or more off the time it takes to really master monads.
This version is 1.3 which has very few small improvements over version 1.2 which contained improved explanations of the List and State monads as well as a bit more detail about monad transformers.
The author has also written ebooks on Git and Javascript. "Git Overview" provides a compact description of Git's more confusing features. "Javascript Promises Clarified" provides a compact description of event loop programming with promises in Javascript.