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

[minh thu]

2009/10/21 Tim Wawrzynczak <inforichland at gmail.com>
>
> 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