[rtpg]

OK, this points out a couple of things that "do not work" in these sorts of situations:

- lazy evaluation with side effects - replacement optimisations based off of referential transparency when there are side effects - general side-effectiness

This is basically saying that functional programming doesn't work when it isn't functional... but we can still have functional "chunks", and monads _are_ an effect system.

I don't really understanding what he's trying to prove, of course purely functional semantics fall apart when side effects are introduced.