On Saturday 31 October 2009 10:50:10 am Daniel Fischer wrote:
Or perhaps he should look at the class IArray from Data.Array.IArray, maybe he can just declare instances of IArray for his datatypes. Without more information, I can't tell which way to go.
Looking into the idea of declaring my types as IArray instances, there's one immediate problem: IArray's only method is "bounds". All of the functions that I want as methods of my class are functions in the IArray module (if I'm reading it correctly). So, it seems like what I want to do is to subclass IArray and add the additional methods. Then I can declare instances for my various types and define the methods appropriately. So, I wrote this: ------------------------------------ import Data.Ix (Ix, inRange) import qualified Data.Array.IArray (IArray, Array, array, listArray, range, bounds, (!)) listArray = Data.Array.IArray.listArray array = Data.Array.IArray.array class (Data.Array.IArray.IArray a e) => MyArray a e where bounds :: Ix i => a i e -> (i,i) range :: Ix i => a i e -> [i] (!) :: Ix i => a i e -> i -> e (//) :: Ix i => a i e -> [(i,e)] type Location = (Int, Int) newtype Board = Board (Data.Array.IArray.Array Location Int) instance MyArray Board where bounds = Data.Array.IArray.bounds (!) = (Data.Array.IArray.!) -------------------------------------- However, the instance declaration gives me a "kind mis-match" error. It says that it expects kind '* -> * -> *', but Board has kind '*'. So, I tried: instance MyArray (Board Data.Array.IArray.Array Location Int) where and other variations on that, but they all give me "Board is applied to too many type arguments". How should this be written? Thanks, Shawn.