[Haskell-cafe] slow code

[Thomas ten Cate]

How much output does this generate? Does it matter if you send the
output to /dev/null? This looks as if the bottleneck might well be in
I/O operations, not in the code itself. To find this out, you could
rewrite the code in C and see if that makes a difference?

Thomas

On Sun, Jun 14, 2009 at 20:44, brian<briand at aracnet.com> wrote:
> Haskell Gurus,
>
> I have tried to use profiling to tell me what's going on here, but it hasn't
> helped much, probably because I'm not interpreting the results correctly.
>
> Empirically I have determined that the show's are pretty slow, so an
> alternative to them would be helpful.  I replaced the show's with "", and
> compiled with -O2 and not much improvement.
>
> I need to write _a lot_ of code in this style.  A few words about how best
> to do this would be helpful.  Laziness, infinite lists, uvector ??
>
> Help...
>
> Thanks,
>
> Brian
>
>
> import Complex
> import System.IO
>
> genData :: Double -> Int -> (Double -> Complex Double) -> ([Double],
> [Complex Double])
> genData tstop n f =
>    let deltat = tstop / (fromIntegral n)
>        t = [ fromIntegral(i) * deltat | i <- [0..n-1]]
>    in
>      (t, map f t)
>
> main =
>    do let (t, y) = genData 100.0E-6 (2 ^ 15) (\x -> x :+ 0.0)
>       h <- openFile "data.txt" WriteMode
>       mapM_ (\(x, y) ->
>                  do hPutStr h (show t)
>                     hPutStr h " "
>                     hPutStrLn h (show (realPart y)))
>                 (zip t y)
>       hClose h
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