[Haskell-cafe] unsafePerformIO: are we safe?

Lennart Augustsson lennart at augustsson.net
Wed Sep 26 14:26:17 EDT 2007

Things can go arbitrarily wrong if you misuse unsafePerformIO, you can even
subvert the type system.

On 9/26/07, Jorge Marques Pelizzoni <jpeliz at icmc.usp.br> 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?
> Thanks in advance. Cheers,
> Jorge.
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