Bjarnasson - scala.io - Purely functional io in scala:
http://blog.higher-order.com/assets/scalaio.pdf
http://www.slideshare.net/InfoQ/purely-functional-io
https://qconnewyork.com/sites/default/files/QConNY2013_RunarBjarnesson_PurelyFunctionalIO.pdf
http://blog.higher-order.com/blog/2013/11/01/free-and-yoneda/