Due to one of the threads on cafe recently, I have been doing some thinking about finalizers. There is this sort of intuitive notion that some things shouldn't be done inside finalizers. For example, no output should be produced, because the output handles may have been finalized already, and finalizers can't be ordered. So, to be safe, the action of a finalizer must commute with every other finalizer (they must be central). And because the finalizers might not be run (compiler can't provide guarantees), their result should not be directly observable, and if the finalizer is not run, the program should still be correct (they must be affine). So a separate ACIO monad for affine central IO actions would be the appropriate context for finalizers. The orignial ACIO proposal was presented in the context of module initalization. http://www.haskell.org//pipermail/haskell-cafe/2004-November/007664.html It strikes me that "module init time" and "finalizer time" are very similar execution contexts. They are 1) outside the normal program flow 2) mostly intended to make the bookeeping work out 3) non-deterministic wrt when/if they will be run 4) if used in the "wrong" ways, they can break program safety. 5) they both are viewed with disfavor for the bad things people can do with them I'm not sure where I am going with this observation, but it seems that if some solution (such as an ACIO monad) could make both of these kinds of action safe, it would probably be worth a second thought.