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

Xiao-Yong Jin xj2106 at columbia.edu
Tue Mar 24 17:34:23 EDT 2009

"Brettschneider, Matthias" <Brettschneider at hs-albsig.de>

> 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?

There shouldn't be any reason.  Try putting

{-# INLINE boundedElems #-}

to make it inline, it might be faster.
    c/*    __o/*
    <\     * (__
    */\      <

More information about the Haskell-Cafe mailing list