Re: [Haskell-cafe] Simple but interesting (for me) problem

2009/10/21 Tim Wawrzynczak

Here's an example in the IO monad:

import Data.IORef import System.IO.Unsafe

counter = unsafePerformIO $ newIORef 0

next = do modifyIORef counter (+1) readIORef counter

Naturally, this uses unsafePerformIO, which as you know, is not kosher...

But you don't close around the Ref like in your schemy example. mkNext = do ref <- newIORef 0 return (do modifyIORef ref succ readIORef ref) mimic your other code better. Cheers, Thu