[Haskell-cafe] Re: unsafePerformIO: are we safe?

Jorge Marques Pelizzoni wrote:

Hi, all!

This is a newbie question: I sort of understand what unsafePerformIO does but I don't quite get its consequences. In short: how safe can one be in face of it? I mean, conceptually, it allows any Haskell function to have side effects just as in any imperative language, doesn't it? Doesn't it blow up referential transparency for good? Is there anything intrinsic to it that still keeps Haskell "sound" no matter what unsafePerformIO users do (unlikely) or else what are the guidelines we should follow when using it?

Old thread, but I don't think anyone mentioned this text from the GHC FAQ: http://haskell.org/haskellwiki/GHC:FAQ#When_is_it_safe_to_use_unsafe_functio... Cheers, Simon