On Fri, Feb 8, 2013 at 1:23 PM, Aleksey Khudyakov <alexey.sklad...@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<http://hackage.haskell.org/package/text>
> [2]
> http://hackage.haskell.org/**package/bytestring<http://hackage.haskell.org/package/bytestring>
>
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