[Haskell-cafe] To my boss: The code is cool, but it is about 100 times slower than the old one...

Fixie Fixie fixie.fixie at rocketmail.com
Thu Nov 29 19:09:33 CET 2012

Hi all haskellers

I every now and then get the feeling that doing my job code in Haskell would be a good idea.

I have tried a couple of times, but each time I seem to run into performance problems - I do lots of heavy computing.

The problem seems to be connected to lazy loading, which makes my programs so slow that I really can not show them to anyone. I have tried all tricks in the books, like !, seq, non-lazy datatypes...

I was poking around to see if this had changed, then I ran into this forum post: http://stackoverflow.com/questions/9409634/is-indexing-of-data-vector-unboxed-mutable-mvector-really-this-slow

The last solution was a haskell program which was in the 3x range to C, which I think is ok. This was in the days of ghc 7.0

I then tried compile the programs myself (ghc 7.4.1), but found that now the C program now was more that 100x faster. The ghc code was compiled with both O2 and O3, giving only small differences on my 64-bit Linux box.

So it seems something has changed - and even small examples are still not safe when it comes to the lazy-monster. It reminds me of some code I read a couple of years ago where one of the Simons actually fired off a new thread, to make sure a variable was realized.

A sad thing, since I am More that willing to go for Haskell if proves to be usable. If anyone can see what is wrong with the code (there are two haskell versions on the page, I have tried the last and fastest one) it would also be interesting.

What is your experience, dear haskellers? To me it seems this beautiful language is useless without a better lazy/eager-analyzer.


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