Quoth Cristiano Paris
I was a bit surprised by the strong reaction about my citation of unsafePerformIO.
Well, there might be a couple of things going on here. Part of it is how to guess the unstated context of a question - I'm fairly sure that given a more thorough presentation of the question, there would have been no controversy about the answer. The general problem is that people who are comfortable with extremely esoteric parts of Haskell and used to discussing such things here, fail to recognize when they're dealing with people who are at a point where their needs are much more basic. (And who knows, which one was the present case? Not really enough information to know absolutely for sure.) But as you have found, unsafePerformIO is not just an esoteric topic, it's an uncomfortable one. We read that it isn't even part of the language, one should never really have any use for it in computation, only as a sort of meta-programming RTS thing. Yet, you might never guess this from reading the GHC documentation, which only urges you to be careful. Or from encountering it in fairly widespread use as a way to implement top level program state with IORefs. This sort of unresolved tension between practice and theory rightly makes people uneasy, and in my opinion you shouldn't take it personally. It's a good thing to occasionally probe those sore spots, and maybe if it bothers us enough it will lead to improvements. Donn