[Haskell-cafe] [Newbie] Cannot derive Eq and Show. Why?

Peter Arrenbrecht peter.arrenbrecht at gmail.com
Fri Sep 8 10:03:36 EDT 2006

Hi all

I am stumped again. The following code generates the error "ERROR
file:.\Cube.hs:12 - An instance of IArray UArray a is required to derive Eq
(Cube a b)" in Hugs. But I did specify the IArray UArray k constraint. So
what is wrong?

module Cube( Cube(..) ) 

import Data.Array.Unboxed

data (Ord k, IArray UArray k, IArray UArray v) =>
	Cube k v 
	= Empty
	| Values (UArray Int k) (UArray Int v)
	| Subs (UArray Int k) (Array Int (Cube k v))

	deriving (Show, Eq)

Thanks for any help
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