Thanks! I was confused at first because ghci still runs into memory problems, though no longer stack overflows. ghc runs it beautifully, though.
-Chad -----Original Message----- From: Amanda Clare [mailto:[EMAIL PROTECTED] Sent: Thursday, July 28, 2005 3:20 AM To: Dean Herington Cc: Scherrer, Chad; haskell@haskell.org Subject: Re: [Haskell] stack overflow - nonobvious thunks? Dean's version certainly seems the neatest, but just for interest you can also do it with a cps fold instead of foldl' too: table xs = assocs $! cpsfold f empty xs where f x m k = case Map.lookup x m of Just v -> v `seq` (k $ Map.adjust (+1) x m) Nothing -> k $ Map.insert x 1 m cpsfold f a [] = a cpsfold f a (x:xs) = f x a (\y -> cpsfold f y xs) As far as I understand it this just makes sure the "seq" happens before the folding continues. When compiled with ghc, both solutions are very well behaved, and seem to take the same small amount of memory whether for 10000000 or 100000000. Amanda Dean Herington wrote: > The following version seems to do the trick (and still remain quite > readable). It worked for 100000000 as well. > > import Data.Map as Map > import System.Random > import Data.List (foldl') > > table :: (Ord a) => [a] -> [(a,Int)] > table xs = Map.assocs $! foldl' f Map.empty xs > where f m x = let m' = Map.insertWith (+) x 1 m > Just v = Map.lookup x m' > in v `seq` m' > > unif :: [Int] > unif = randomRs (1,10) $ mkStdGen 1 > > f :: Int -> [(Int, Int)] > f n = table $ take n unif > main = print $ f 10000000 > > - Dean _______________________________________________ Haskell mailing list Haskell@haskell.org http://www.haskell.org/mailman/listinfo/haskell
