a slight modification to compile it : change: where sumFile = sum . map read . L.words to : where sumFile = sum . map (read . L.unpack) . L.words but it's actually _slower_ than the non-bytestring version. i did a little test, three versions of the same script and manufactured meself a ~50 MB file containing 1M of ints 0-65535. and replaced the sum with length for obvious reasons. module Main where import qualified Data.ByteString.Lazy.Char8 as L main1 = do contents <- L.getContents print (sumFile contents) where sumFile = length . map L.readInt . L.words main2 = do contents <- getContents print (sumFile contents) where sumFile = length . map (read :: String -> Int) . words main3 = do contents <- L.getContents print (sumFile contents) where sumFile = length . map ((read :: String -> Int) . L.unpack) . L.words time main3 < nums real 0m22.421s user 0m0.031s sys 0m0.000s time main2 < nums real 0m14.296s user 0m0.015s sys 0m0.016s time main1 < nums real 0m22.078s user 0m0.015s sys 0m0.015s i expected the conversions (L.unpack in main3) to kill the performance a little, but not to make it nearly two times as slow. and i certainly did not expect that even the version using the bytestring readInt to be as slow ... did I do something wrong ? On Tue, Oct 7, 2008 at 4:06 AM, Mike Coleman <tutufan@gmail.com> wrote:
Hi,
I could use a little help. I was looking through the Real World Haskell book and came across a trivial program for summing numbers in a file. They mentioned that that implementation was very slow, as it's based on String's, so I thought I'd try my hand at converting it to use lazy ByteString's. I've made some progress, but now I'm a little stuck because that module doesn't seem to have a 'read' method.
There's a readInt method, which I guess I could use, but it returns a Maybe, and I don't see how I can easily strip that off.
So:
1. Is there an easy way to strip off the Maybe that would allow an equivalently concise definition for sumFile? I can probably figure out how to do it with pattern matching and a separate function--I'm just wondering if there's a more concise way.
2. Why doesn't ByteString implement 'read'? Is it just that this function (like 'input' in Python) isn't really very useful for real programs?
3. Why doesn't ByteString implement 'readDouble', etc.? That is, why are Int and Integer treated specially? Do I not need readDouble?
Thanks, Mike
-- lazy version (doesn't compile)
-- file: ch08/SumFile.hs
import qualified Data.ByteString.Lazy.Char8 as L
main = do contents <- L.getContents print (sumFile contents) where sumFile = sum . map read . L.words _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe