Re: [Haskell-cafe] How to think about this? (profiling)

This is actually a perfect case for lazy immutable arrays, if you use a circular program:

import Data.Array

foo' :: Array Int Int -> Int -> Int foo' arr 0 = 0 foo' arr 1 = 1 foo' arr 2 = 2 foo' arr n = arr!(n-1) + arr!(n-2) + arr!(n-3)

foo :: Int -> Int foo n = arr ! n where assocs = [(i, foo' arr i) | i <- [0..n]] arr = array (0,n) assocs

But I haven't checked its performance against your version, so I don't know how good it is. / Emil Magnus Therning skrev:

On Tue, Dec 16, 2008 at 12:14 PM, Lemmih wrote:

...

You could use a Map or a mutable array. However, this kind of problem comes up a lot less often than you'd think.

Well, I happen to have a problem just like it right now, hence my interest :-) In order to better understand the different options I thought I'd look at solving simpler problems with similar "shape".

Thanks for pointing me in the direction of mutable arrays, I haven't explored those before.

/M