Adrian, Does your AVL library have an "insertWith'"-type function mentioned by Udo? If I lookup and insert into the table separately, forcing evaluation at each step, I can do table' :: (Ord a) => [a] -> [(a, Int)] table' xs = Map.assocs $! foldl' f Map.empty xs where f m x = (Map.insert x $! 1 + Map.findWithDefault 0 x m) $! m This helps with the stack overflow problem, but now I'm hitting a different wall: *Main> table $ take 10000000 unif [(1,999662),(2,1000220),(3,998800),(4,1000965),(5,999314),(6,1001819),(7 ,1000997),(8,999450),(9,999877),(10,998896)] *Main> table $ take 100000000 unif <interactive>: out of memory (requested 1048576 bytes) I thought I may have found a good approach using an idea from one of Amanda Clare's pages http://users.aber.ac.uk/afc/stricthaskell.html If I write eqSeq x y = if x==x then y else y this forces evaluation of x further than seq alone. Then I can write table :: (Ord a) => [a] -> [(a, Int)] table xs = Map.assocs $! foldl' f Map.empty xs where f m x = m `eqSeq` Map.insertWith (+) x 1 m Same result as Udo's suggestion - out of memory. I still don't see why this function should need any more than a few kilobytes, even for very large n like this. -Chad -----Original Message----- From: u.stenzel@web.de [mailto:u.stenzel@web.de] Sent: Wednesday, July 27, 2005 11:02 AM To: Scherrer, Chad Cc: haskell@haskell.org Subject: Re: [Haskell] stack overflow - nonobvious thunks? Scherrer, Chad wrote:
f m x = Map.insertWith (+) x 1 m
insertWith is inserting the "nonobvious thunks". Internally it applies (+) to the old value and the new one, producing a thunk. There is no place you could put a seq or something to force the result. You basically need insertWith', which isn't there. I think, your best best is to manually lookup the old value, combine with the new, force the result, then insert that, overwriting the old value. On top of that you still need foldl' to avoid building long chains of Map.insert. Udo. -- The Second Law of Thermodynamics: If you think things are in a mess now, just wait! -- Jim Warner