But how can you tell something being causal or not? Assuming that all IO operations return random result, of course. :)
>From a practical point of view unsafeInterleaveIO can give suspect results. But theoretically you can't fault it until you have given a semantics for the IO monad operations so you have something to compare it against. -- Lennart On Thu, Nov 13, 2008 at 12:05 AM, Jonathan Cast <[EMAIL PROTECTED]> wrote: > On Wed, 2008-11-12 at 18:47 -0500, Dan Doel wrote: >> On Wednesday 12 November 2008 6:18:38 pm David MacIver wrote: >> > To put it a different way, in the absence of unsafeInterleaveIO the IO >> > monad has the property that if f and g are observably equal up to >> > termination then x >>= f and x >>= g are equivalent in the IO monad >> > (actually this may not be true due to exception handling. Our three >> > main weapons...). In the presence of unsafeInterleaveIO this property >> > is lost even though referential transparency is retained. >> >> I'm not sure what exactly you mean by this, but, for instance: >> >> randomIO >>= (print :: Int -> IO ()) >> >> obviously isn't going to give the same results as: >> >> randomIO >>= (print :: Int -> IO ()) >> >> every time. Your weirdTuple is semantically similar, in that it selects >> between returning (1,1) and (2,1), but instead of being random, it >> operationally selects depending on how you subsequently evaluate the value. > > I think the point is that randomIO is non-deterministic (technically, > pseudo-random) but causal --- the result is completely determined by > events that precede its completion. unsafeInterleaveIO, by contrast, is > arguably (sometimes) deterministic --- but is, regardless, definitely > not causal. > > jcc > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
