> For clarity, one trick that uses "unsafePerformIO" which you may have seen
> posted on this list earlier today is the following way of creating a
> globally visible IORef:
>
> import Data.IORef
> import System.IO.Unsafe
>
> *** counter = unsafePerformIO $ newIORef 0 ***
>
> next = do
> modifyIORef counter (+1)
> readIORef counter
This is still unsafe but it can evidently be slightly improved with
NOINLINE pragma:
{-# NOINLINE counter #-}
counter = unsafePerformIO $ newIORef 0
without said pragma the counter could be initialized numerous times,
as I understand it. All this said, I hope people avoid
unsafePerformIO for mutable globals - reader monad, state monad, and
partial application should be sufficient tools.
Thomas
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