Array optimisation...

[Josef Svenningsson]

On Mon, 23 Feb 2004, MR K P SCHUPKE wrote:

>
> Was just thinking about GHC's implementation of arrays, and their
> poor performance. I know little about GHC's internal workings, but
> I was thinking about how array performance could be improved.
>
> What if when writing an array you instead construct a function:
>
> f :: (Ix x,Ix y) => Array a -> Ix x -> a -> Ix y -> a
> f a x b y | x==y = b
>           | otherwise = a!y
>
> Then the update in place operator // becomes a curried application
> of 'f' above.
>
> You could then define a a series of 'overlays' for a base array.
> The clever bit would be to get the garbage collector to merge
> the two as soon as any reference to the original array is
> discarded.
>
> Does GHC already do anything like this?
>
No it doesn't. But if you want this behaviour you should look at
Data.Array.Diff . I think that library does what you want.

Cheers,

	/Josef