Hello Adrian, On 3/6/06, Adrian Hey wrote:

Hello Jean-Philippe,

I haven't had much time to study this, but in the light of recent discussions about generalised tries I played about a little last night and did have a go at producing n-Tuple maps from instances of your classes. e.g. for pairs I ended up trying to define something like this..

instance (MapLike c1 k1 c2, MapLike c2 k2 a) => MapLike (Map2 c1) (k1,k2) a where..

Not sure I got what you want to do exactly, but here's what I came up with: (using Indexed because it's lighter, but the idea is the same for Map.) module Map2 where import Data.Collections newtype Map2 c1 c2 k1 k2 v2 = Map2 c1 instance (Indexed c1 k1 c2, Indexed c2 k2 v2) => Indexed (Map2 c1 c2 k1 k2 v2) (k1,k2) v2 where (!) (Map2 c1) (k1,k2) = (c1 ! k1) ! k2

I must admit I found it hard going, but maybe I'm just using it wrong and I didn't have much time to play about with alternatives. Perhaps you'd care to give it a shot.

You "just" need to witness the types you define Map2 for as parameters. A bit tricky, I grant you, but nonetheless logical. Once I got used to it I didn't find it any more difficult than the constructor-class approach. Cheers, JP.