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
