> Actually, I kind of wish IO was split up a bit... I have been meaning to play with rolling some typeclasses (with an IO instance and a testing instance) that wrap up IO of various types, so I define my functions in terms of these and spot what kind of IO various functions might do - I'm not yet sure how much of a win it will be, but it seems like something to explore.

There's a section on this practice in Real World Haskell: http://book.realworldhaskell.org/read/programming-with-monad...