Thanks guys, I thinks I can stop trying to get things out of IO now. Instead I should see if I could make my monad as an instance of MonadIO, so I can use liftIO, which should be safe I believe.

2011-5-6下午3:46，Daniel Fischer <daniel.is.fischer@googlemail.com>撰写：
> On Friday 06 May 2011 05:28:35, Felipe Almeida Lessa wrote:
>
> > If you are a beginner, you should never use anything that starts with
>
> > 'unsafe'.
>
>
>
> Basically yes, use something beginning with 'unsafe' only when you know why
>
> it's not unsafe in your specific case.
>
>
>
> But of course there are different levels of unsafeness,
>
> Data.Array.Base.unsafeAt for example is relatively benign (same as in other
>
> languages: if you don't let the compiler check array bounds and screw your
>
> check up, you can get nonsense or segfaults, but it's relatively easy to
>
> understand and control).
>
>
>
> > And you should never use 'unsafePerformIO'. And you
>
> > should NEVER use 'unsafeCoerce'.
>
>
>
> Those two indeed have a different calibre, use them only
>
> whenYouReallyKnowWhatYouAreDoing.
>
>
>
> They have their uses and sometimes are the right thing, but like goto, in
>
> most cases one is tempted to use them, one shouldn't.
>
>
>
> >
>
> > Cheers, =)
>
> >
>
> > --
>
> > Felipe.
>