Implementations of Ix methods in terms of Enum methods.

For a type T of class Enum you can easily define an Ix instance by copying the following code into your module:

import qualified Data.Ix.Enum as IxEnum

instance Ix T where
   range           = IxEnum.range
   index           = IxEnum.index
   inRange         = IxEnum.inRange
   rangeSize       = IxEnum.rangeSize
   unsafeIndex     = IxEnum.unsafeIndex
   unsafeRangeSize = IxEnum.unsafeRangeSize