Hi, I was wondering what the best way to implement Natural number would be. Is there a package which already does this? Here are some options: 1. Don’t bother. Just use Integer. 2. Use the type data Natural = Zero | Succ !Natural 3. Use the following definition taken from the Gentle Introduction to Haskell 98 newtype Natural = MakeNatural Integer toNatural ::Integer-> Integer toNatural x | x < 0 = error “Can’t create negative naturals!” | otherwise = MakeNatural x fromNatural :: Natural -> Integer fromNatural (MakeNatural i) = i and then... instance Num Natural where fromInteger = toNAtural x + y = toNatural (fromNatural x + fromNatural y) x – y = etc.. x * y = etc... Which method is best? So far, I’ve been picking option #1 – just leaving things as they are and using Integer to keep things simple. I’ve got that feeling that [2] would be fast and [3] would be slow. Comment appreciated on the merits of each. Cheers, Mark Spezzano No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.12/1998 - Release Date: 12/03/2009 6:23 PM