IO functional side effects

https://www.infoq.com/presentations/io-functional-side-effects

The algebra of algebraic data types

http://chris-taylor.github.io/blog/2013/02/10/the-algebra-of-algebraic-data-types/

Free and CoFree monads in Scala

http://underscore.io/blog/posts/2015/04/14/free-monads-are-simple.html
https://softwaremill.com/free-monads/
https://blog.scalac.io/2016/06/02/overview-of-free-monad-in-cats.html
http://typelevel.org/cats/datatypes/freemonad.html
http://degoes.net/articles/easy-monads
http://eed3si9n.com/herding-cats/stackless-scala-with-free-monads.html
http://blog.higher-order.com/assets/trampolines.pdf