On 23/09/2009 18:46, Roel van Dijk wrote:
This might be "dirty" but what about this instead?
instance (NFData a) => NFData (Data.IORef.IORef a) where rnf r = unsafePerformIO $ modifyIORef r (`using` rnf)
Hmm, I don't know. The question is whether you want to evaluate the value stored inside of the IORef. I think that any function that evaluates a value inside of an IORef should be in the IO monad. I wouldn't expect a function with the type "a -> ()" to be able to "look into" an IORef.
The reason I made an NFData instance for IORef is for a situation like this:
test :: IO () test = do x<- newIORef () y<- newIORef () let z | hugeConditionalExpression = x | otherwise = y rnf z `seq` doSomething
You might want to force z to head normal form to force the evaluation of the hugeConditionalExpression.
what's wrong with instance NFData (Data.IORef.IORef a) where rnf r = r `seq` () ? Cheers, Simon