Put a bang pattern on your accumulator in "go". Since the value is not demanded until the end of the program, you're actually just building up a huge space leak there.
Secondly, unconsing from the lazy bytestring will cause a lot of allocation churn in the garbage collector -- each byte read in the input forces the creation of a new "L.ByteString", which is many times larger. Also please consider trying the "io-streams" library that I wrote ( http://hackage.haskell.org/package/io-streams). It provides primitives for streaming IO in "basic Haskell" style. To provide a Word8 stream (which is probably a bad idea performance-wise) it would be most efficient allocation-wise to implement a mutable index cursor (i.e. IORef Int) that pointed to your current position within the ByteString chunk, other strategies will probably allocate too much. G On Mon, Mar 18, 2013 at 9:53 AM, Konstantin Litvinenko < to.darkan...@gmail.com> wrote: > Hi All! > > I tune my toy project for performance and hit the wall on simple, in > imperative world, task. Here is the code that model what I'm trying to > achieve > > import qualified Data.ByteString.Lazy as L > import Data.Word8(isSpace) > import Data.Word > import Control.Monad.State > > type Stream = State L.ByteString > > get_byte :: Stream (Maybe Word8) > get_byte = do > s <- get > case L.uncons s of > Nothing -> return Nothing > Just (x, xs) -> put xs >> return (Just x) > > main = do > f <- L.readFile "test.txt" > let r = evalState count_spaces f > print r > where > count_spaces = go 0 > where > go a = do > x <- get_byte > case x of > Just x' -> if isSpace x' then go (a + 1) else go a > Nothing -> return a > > It takes the file and count spaces, in imperative way, consuming bytes one > by one. The problem is: How to rewrite this to get rid of constant > allocation of state but still working with stream of bytes? I can rewrite > this as one-liner L.foldl, but that doesn't help me in any way to optimize > my toy project where all algorithms build upon consuming stream of bytes. > > PS. My main lang is C++ over 10 years and I only learn Haskell :) > > > ______________________________**_________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/**mailman/listinfo/haskell-cafe<http://www.haskell.org/mailman/listinfo/haskell-cafe> > -- Gregory Collins <g...@gregorycollins.net>
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe