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. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
