[Haskell-cafe] RE: [Haskell] line-based interactive program

On 08 July 2005 18:22, Olaf Chitil wrote:

In fact, unsafeInterleaveIO shows up limitations of the IO monad. Without this strange primitive (what is actually unsafe about it?)

Just picking up on this point: unsafeInterleaveIO is so named because it lets you write programs that don't obey the usual laws. For example: main = do r <- newIORef 0 a <- unsafeInterleaveIO $ readIORef r b <- unsafeInterleaveIO $ do writeIORef r 42; return 0 print (a + b) if you change (a + b) to (b + a), you get a different answer. Cheers, Simon