> Here’s the deal: Haskell doesn’t allow side-effects. At all.

I disagree with this, and it was Eric Meijer's "Fundamentalist Functional Programming" lecture that really changed my mind. The point isn't that Haskell prevents side effects. It's that it requires you to be explicit about them. Indeed, some advocates say that Haskell is "the best imperative langauge". I don't know that I would go that far though.