On 25 June 2004 15:09, Daan Leijen wrote:

Ok, I never thought of that. However, isn't it the case that I normally just want to get the old value back? In that case, the current interface is not so friendly.

Is anyone using this function to get something else than the old/new value *and* where the computation is expensive?

If not, maybe we should (also) provide a nicer interface?

I've no objection to providing simpler versions of the more general interface - in fact I believe we discussed this when atomicModifyIORef was introduced. How about: atomicModifyIORef_ :: IORef a -> (a -> a) -> IO a atomicModifyIORef_ r f = atomicModifyIORef r (\a -> (f a, a)) If this turned out to be a common case that needs to be fast, then we can implement it using a primitive in GHC. Cheers, Simon