Hi, from the GHC documentation (5.17.1 in the libraries section), I get the impression that (!) is a member of the IArray class. While I'm messing about with kinds and stuff getting this properly instantiated, I get an error claiming that EST.lhs:44: Class `IArray' does not have a method `!' In the instance declaration for `IArray EST n' Experimenting with GHCi, I finally worked out Prelude> :i IArray.IArray -- ArrayBase.IArray is a class class (ArrayBase.HasBounds a) => ArrayBase.IArray a :: (* -> * -> *) e where { ArrayBase.unsafeArray :: forall i. (PrelArr.Ix i) => (i, i) -> [(Int, e)] -> a i e; ArrayBase.unsafeAt :: forall i. (PrelArr.Ix i) => a i e -> Int -> e; ArrayBase.unsafeReplace :: forall i. (PrelArr.Ix i) => a i e -> [(Int, e)] -> a i e {- has default method -}; ArrayBase.unsafeAccum :: forall e' i. (PrelArr.Ix i) => (e -> e' -> e) -> a i e -> [(Int, e')] -> a i e {- has default method -}; ArrayBase.unsafeAccumArray :: forall e' i. (PrelArr.Ix i) => (e -> e' -> e) -> e -> (i, i) -> [(Int, e')] -> a i e {- has default method -}; } So, unless I'm misinterpreting something, the documentation is incorrect? What I'd like to have, is Int-indexed access to my classes. ATM, I've solved it with my own class "Indexed" providing a (?) operator. This is (obviously) not consistent with the standard types, and in addition collides slightly with the implicit parameters syntax (works if I leave a space between the ? and the index) -kzm -- If I haven't seen further, it is by standing in the footprints of giants