Re: [Haskell-cafe] Efficient functional idiom for histogram

2009/8/1 Ketil Malde :

Paul Moore writes:

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What am I doing wrong here? I'd have expected compiled Haskell to be faster than interpreted Python, so obviously my approach is wrong.

Two things from my experience: Python associative arrays are fast, and Haskell random numbers are slow.  So by building a map from random numbers, you are likely doing a fairly pessimal comparison.

Hmm, I think you're saying that for this problem, Haskell is likely to be worse than Python. Interesting. I guess I'd assumed that something CPU-intensive like this would benefit from a compiled language. Just goes to show that intuition about performance is usually wrong (something I really should know by now :-)) Is the issue with random numbers just the implementation, or is it something inherent in the non-pure nature of a random number generator that makes it hard for Haskell to implement efficiently? If the latter, that probably makes Haskell a somewhat poor choice for simulation-type programs.

Did you profile to see where the time is spent?

Not until you suggested it :-) I was pleasantly surprised by how easy it was to do. The results bear out what you were saying, the bottleneck is entirely in the "dice" function.

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I'm expecting the answer to be that I've got unnecessary laziness

IME, laziness usually affects space, but not so much time performance.  Although 'insertWith (+)' looks like it would build unevaluated thunks for the sums.

That'll teach me to bandy about technical terms as if I understand them :-) Thanks for the comments, Paul.