A bunch of interesting links to understand Functional IO in Scala from scratch.
"IO is the trickiest of operations to tackle in a functional way. Try to make IO efficient, non-leaky, composable, and pure, and the problem becomes virtually unsolvable. In this talk, John A. De Goes, CTO of ReportGrid, discusses three different approaches to functional IO in Scala, beginning with iteratees, and continuing on to stream processors and transducers."
Learn about Efficient Functional IO in Scala (presentation from Northeast Scala Symposium)
Towards an Effect System in Scala, Part 2: IO Monad
GGHF.