On Wed, 2008-11-12 at 23:18 +0000, David MacIver wrote: > On Wed, Nov 12, 2008 at 11:05 PM, Jonathan Cast > <[EMAIL PROTECTED]> wrote: > > On Wed, 2008-11-12 at 23:02 +0000, David MacIver wrote: > >> On Wed, Nov 12, 2008 at 10:46 PM, Don Stewart <[EMAIL PROTECTED]> wrote: > >> > david.maciver: > >> >> On Wed, Nov 12, 2008 at 8:35 PM, Lennart Augustsson > >> >> <[EMAIL PROTECTED]> wrote: > >> >> > Actually, unsafeInterleaveIO is perfectly fine from a RT point of > >> >> > view. > >> >> > >> >> Really? It seems easy to create things with it which when passed to > >> >> ostensibly pure functions yield different results depending on their > >> >> evaluation order: > >> >> > >> >> module Main where > >> >> > >> >> import System.IO.Unsafe > >> >> import Data.IORef > >> >> > >> >> main = do w1 <- weirdTuple > >> >> print w1 > >> >> w2 <- weirdTuple > >> >> print $ swap w2 > >> >> > >> >> swap (x, y) = (y, x) > >> >> > >> >> weirdTuple :: IO (Int, Int) > >> >> weirdTuple = do it <- newIORef 1 > >> >> x <- unsafeInterleaveIO $ readIORef it > >> >> y <- unsafeInterleaveIO $ do writeIORef it 2 >> return 1 > >> >> return (x, y) > >> >> > >> >> [EMAIL PROTECTED]:~$ ./Unsafe > >> >> (1,1) > >> >> (1,2) > >> >> > >> >> So show isn't acting in a referentially transparent way: If the second > >> >> part of the tuple were evaluated before the first part it would give a > >> >> different answer (as swapping demonstrates). > >> > > >> > Mmmm? No. Where's the pure function that's now producing different > >> > results? I only see IO actions at play, which are operating on the > >> > state of the world. > >> > >> I suppose so. The point is that you have a pure function (show) and > >> the results of evaluating it totally depend on its evaluation order. > > > > Sure. But only because the argument to it depends on its evaluation > > order, as well. > > That's not really better. :-)
I never said it was. jcc _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
