[Haskell-cafe] OCaml list sees abysmal Language Shootout results

[Georg Martius]

On Wed, 29 Sep 2004 15:58:24 -0700, Greg Buchholz <haskell at sleepingsquirrel.org> 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

-- 

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