On Wed, 29 Sep 2004 15:58:24 -0700, Greg Buchholz <[EMAIL PROTECTED]> wrote:
<snip>
Just for the heck of it, I'd thought I'd try to write a naive 1-pass version of the program. It turned out to be 4.5 times slower than the original...
-- compiled with: ghc -O2 -ddump-simpl -fvia-c -o wc_fold wc_fold.hs
import IO
main = do file <- getContents putStrLn (show (foldl wc (0,0,0) file))
wc :: (Int,Int,Int) -> Char -> (Int, Int, Int) wc (l,w,c) '\n' = (l+1,w ,c+1) wc (l,w,c) ' ' = (l ,w+1,c+1) wc (l,w,c) x = (l ,w ,c+1)
use strictness is the trick to exploit the tail-recursion. There is possibly a better way but:
data C = C !Int !Int !Int deriving Show wc' :: C -> Char -> C wc' (C l w c) '\n' = C (l+1) w (c+1) wc' (C l w c) ' ' = C l (w+1) (c+1) wc' (C l w c) x = C l w (c+1)
is significant faster. The results on a 12MB file:
original:
1,699,541,396 bytes allocated in the heap
340,796,888 bytes copied during GC
75,415,872 bytes maximum residency (8 sample(s))
146 Mb total memory in use
Total time 5.92s ( 6.09s elapsed)wc: (yours)
I have not enough memory :-(
wc':
535,286,872 bytes allocated in the heap
187,340,032 bytes copied during GC
135,696 bytes maximum residency (130 sample(s))
2 Mb total memory in use
Total time 2.45s ( 2.53s elapsed)Cheers, Georg
--
---- Georg Martius, Tel: (+49 34297) 89434 ---- ------- http://www.flexman.homeip.net --------- _______________________________________________ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
