I have a simple program that first generates a large (~ 500 mb) file of random numbers and then reads the numbers back to find their sum. It uses Data.Binary and Data.ByteString.Lazy. The problem is when the program tries to read the data back it quickly (really quickly) consumes all memory. The source: http://moonpatio.com/fastcgi/hpaste.fcgi/view?id=3607#a3607 or: module Main where import Data.Binary import Data.Int import System.Random import qualified Data.ByteString.Lazy as BL encodeFileAp f = BL.appendFile f . encode path = "Results.data" n = 20*1024*1024 :: Int getBlockSize :: BL.ByteString -> Int64 getBlockSize bs = round $ (fromIntegral $ BL.length bs) / (fromIntegral n) fillFile :: StdGen -> Int -> IO () fillFile _ 0 =return () fillFile gen i = do let (x, gen') = random gen :: (Double, StdGen) encodeFileAp path x fillFile gen' (i-1) processFile :: BL.ByteString -> Int64 -> Int -> Double -> Double processFile bs blockSize 0 sum = sum processFile bs blockSize i sum = let tmpTuple = BL.splitAt blockSize bs x = decode $ fst $! tmpTuple in processFile (snd tmpTuple) blockSize (i-1) $! sum + x main = do fillFile (mkStdGen 42) n results <- BL.readFile path putStrLn $ show $ processFile results (getBlockSize results) n 0