On Fri, Feb 8, 2013 at 1:23 PM, Aleksey Khudyakov <alexey.skladnoy@gmail.com> wrote:

On 08.02.2013 23:26, Nicolas Bock wrote:

Hi list,

I wrote a script that reads matrix elements from standard input, parses
the input using a regular expression, and then bins the matrix elements
by magnitude. I wrote the same script in python (just to be sure :) )
and find that the python version vastly outperforms the Haskell script.

General performance hints

1) Strings are slow. Fast alternatives are text[1] for textual data and bytestrings[2] for binary data. I can't say anything about performance of Text.Regex.Posix.

Hi Aleksey,

could you show me how I would use ByteString? I can't get the script to compile. It's complaining that:

No instance for (RegexContext

Regex Data.ByteString.ByteString (AllTextSubmatches [] a0))

which is too cryptic for me. Is it not able to form a regular expression with a ByteString argument? From the documentation of Text.Regex.Posix it seems that it should be. Maybe it's because I am trying to "read (r!!1) :: Double" which I am having issues with also. Is (r!!1) a ByteString? And if so, how would I convert that to a Double?

Thanks,

nick

2) Appending list wrong operation to do in performance sensitive code.
(++) traverses its first argument so it's O(n) in its length.

What exactly are you tryeing to do? Create a histogram?

The Haskell script was compiled with "ghc --make printMatrixDecay.hs".

If you want performance you absolutely should use -O2.

[1] http://hackage.haskell.org/package/text
[2] http://hackage.haskell.org/package/bytestring

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