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 <[EMAIL PROTECTED]> 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
>
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