16 Nov
2011
16 Nov
'11
5:42 p.m.
On Wed, Nov 16, 2011 at 2:23 PM, Jason Dusek
Just double checked. modifySTRef is too lazy: -- |Mutate the contents of an 'STRef' modifySTRef :: STRef s a -> (a -> a) -> ST s () modifySTRef ref f = writeSTRef ref . f =<< readSTRef ref We need Data.STRef.Strict
Tried a modifySTRef' defined this way:
modifySTRef' ref f = do val <- (f $!!) <$> readSTRef ref writeSTRef ref (val `seq` val)
...but there was no change in memory usage.
Why not just modifySTRef :: STRef s a -> (a -> a) -> ST s () modifySTRef ref f = do x <- readSTRef ref writeSTRef ref $! f x (Note that I didn't check if modifySTRef was actually a problem in this case). -- Johan