On Friday 01 June 2007, Andrew Coppin wrote: > David Roundy wrote: > > Note also that you can use unsafePerformIO to safely get pure functions > > doing both these operations. > > I've always been puzzled by this one... how does unsafePerformIO > circumvent the type system? I don't understand.
import Data.IORef import System.IO.Unsafe ref :: IORef a ref = unsafePerformIO $ newIORef undefined cast :: a -> b cast a = unsafePerformIO $ do writeIORef ref a ; readIORef ref *Main> cast 2 :: Double -3.824225156758791e-48 *Main> -- Dan _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
