Hello Chris, Friday, March 17, 2006, 10:31:28 PM, you wrote: CK> If I may make a suggestion: I think you have identified a need for certain CK> operations which would benefit from a typeclass. The dynamic arrays need new CK> operations on their indices, so they need a more specific type than Ix: the *small* problem is what writeArray and all other operations defined with Ix in its head, so it's impossible to use in implementation any operations not in the Ix dictionary! The problem, after all, is what the MArray typeclass DON'T INCLUDES index type ibn its head, so i can't define something like: instance (IxDynamic i) => MArray DynamicIOArray i e IO ... and NOT making dynamic arrays an MArray instance is total useless in my opinion (and at least can be done by anyone without changing the arrays library). on the other side, changing MArray interface arity (number of parameters) will lead to changing declarations for all routines what acquire MArray parameters. so i still look for more oldcode-compatible solutions -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com