[Haskell-cafe] Haskell performance question

[Bulat Ziganshin]

Hello Dan,

Thursday, November 8, 2007, 9:33:12 PM, you wrote:

> main = do
>    a <- newArray (0,n-1) 1.0 :: IO (IOUArray Int Double)
>    forM_ [0..n-2] $ \i -> do { x <- readArray a i; y <- readArray a
> (i+1); writeArray a (i+1) (x+y) }
>    x <- readArray a (n-1)
>    print x

1. ghc doesn't implement loop unrolling, even in -O2 mode
2. forM_ may have its own overheads, i'm not sure
3. add strictness annotations:

forM_ [0..n-2] $ \i -> do { return $! i;
                            x <- readArray a i; return $! x;
                            y <- readArray a (i+1); return $! y;
                            writeArray a (i+1) (x+y) }

such cycle should be approx. 3-10 times slower than C one

-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin at gmail.com