> 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
(Note that I didn't check if modifySTRef was actually a problem in this case).