On Fri, 2007-06-22 at 09:38 +1000, Thomas Conway wrote:
The actual case that I'm dealing with, where I believe Data.Map (or similar, incl finger trees) has a benefit is one in which it's not simply a case of lists of items, yielding a list of items. I'm manipulating an on-disk inverted index, so rather than a simple list of items, the code is actually monadic, doing IO to retrieve the items off disk, and the cost of creating the intermediate lists is unwearable. The key problem is that you loose the laziness because of the IO monad, so if you're not careful, you end up trying to store the complete intermediate lists.
You might find that lazy IO is helpful in this case. The primitive that implements lazy IO is unsafeInterleaveIO :: IO a -> IO a Note that using a Map will probably not help since it needs to read all the keys to be able to construct it so that'd pull in all the data from disk. Duncan