Thanks for pointing to "type level integers". With that I have found: http://www.haskell.org/haskellwiki/The_Monad.Reader/Issue5/Number_Param_Type... For example: ------------------------------- data Zero = Zero data Succ a = Succ a class Card c where c2num:: c -> Integer cpred::(Succ c) -> c cpred = undefined instance Card Zero where c2num _ = 0 instance (Card c) => Card (Succ c) where c2num x = 1 + c2num (cpred x) main = do putStrLn $ show $ c2num (Succ (Succ Zero)) ------------------------------- I will continue to examine the topic in the following days, according to my needs. Thanks a lot, TP On Sunday, April 28, 2013 07:58:58 Stephen Tetley wrote:
What you probably want are type level integers (naturals)
Yury Sulsky used them in the message above - basically you can't use literal numbers 1,2,3,... etc as they are values of type Int (or Integer, etc...) instead you have to use type level numbers:
data One data Two
Work is ongoing for type level numbers in GHC and there are user libraries on Hackage so there is a lot of work to crib from.