Hello, I am working on an Ix instance for one of my types and finding it rather restrictive. For me it would be useful to have rangeSize be defined in the Ix class (with a default definition of course), so that it can be overridden. Also, does anybody know why Ix derives from Ord? It seems to me this is an unnecessary limitation on the types that can be instances of Ix. I cannot think of a reason why the implementation of anything in the Ix or Array modules would require that every Ix be an Ord (with a minor exception -- see below). If an implementation is using a comparison on an Ix type, chances are it should be using inRange or comparing (index bnds x) with (index bnds y) instead. One change would have to be made in the Array module if Ord is removed from Ix: instance (Ix a, Eq b) => Eq (Array a b) where a == a' = assocs a == assocs a' instance (Ix a, Ord b) => Ord (Array a b) where a <= a' = assocs a <= assocs a' would become: instance (Ix a, Eq a, Eq b) => Eq (Array a b) where a == a' = assocs a == assocs a' instance (Ix a, Ord a, Ord b) => Ord (Array a b) where a <= a' = assocs a <= assocs a' As I said, I think this is a very minor issue. I believe that making these changes in the standard would not impact existing programs in any way. Could these changes be considered as a possible "typo" to be fixed in the Library Report? P.S. In case anybody's interested, here's why I want to override rangeSize:
newtype Honeycomb = Hx (Int,Int) deriving (Eq,Show,Ord)
indexError = error "Index out of range"
instance Ix Honeycomb where range (Hx b1, Hx b2) = [Hx x | x <- range (b1,b2), isHexIx x] inRange (Hx b1, Hx b2) (Hx x) = inRange (b1,b2) x && isHexIx x index (Hx b1, Hx b2) (Hx x) = let i = index (b1,b2) x in if isHexIx x then i `div` 2 else indexError
isHexIx :: (Int,Int) -> Bool isHexIx (x,y) = x `mod` 2 == y `mod` 2
This implements a honeycomb or hexagonal tiling for a maze generating program. The honeycomb is superimposed on a grid such that only every other square is "active", corresponding to a particular hexagon in the honeycomb. It's similar to a checkers game, where only the dark squares are used. I would like _any_ pair of Ints to be an acceptable boundary for the honeycomb, not just the ones that represent valid indexes. For example, (Hx (0,0), Hx (15,12)) should be a valid set of bounds. The current definition of rangeSize makes this impossible, which is why I would like to override it. By the way, the Library Report does not explicitly say that the bounds have to both be valid indexes, though it does imply this with the sample definition of rangeSize. Thanks, Matt Harden