[Haskell-cafe] Are there performant mutable Arrays in Haskell?

Brettschneider, Matthias Brettschneider at hs-albsig.de
Tue Mar 24 05:03:49 EDT 2009

Thx for your hints, I played around with them and the performance gets slightly better. 
But the major boost is still missing :) 

I noticed, that one real bottleneck seems to be the conversion of the array back into a list. 
The interesting part is, if I use the elems function (Data.Array.Base) the performance is about
4x better then with my own function. So I thought, I write my own version of elems, (that just converts
a part of the array to a list) and I fall back into the same performance as my first approach. 

To make a long story short, here is the library code: 
elems arr = case bounds arr of
      (_l, _u) -> [unsafeAt arr i | i <- [0 .. numElements arr - 1]

And my version:
boundedElems arr = case bounds arr of
      (_l, _u) -> [unsafeAt arr i | i <- [1737 .. 1752]]

Is there a reason, why the library version is 4 times faster, than mine?

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