Re: [Haskell-beginners] Enum for natural numbers

2009/12/21 :

Now everything works but to print Z also for negative Integers. Don't know how to implement the <=0 or le0 in this case again:

instance Enum Nat where        toEnum 0 = Z        toEnum (n+1) = S(toEnum n)        fromEnum Z = 0        fromEnum (S n) = 1 + fromEnum n

Again, look into guards. You are definitely on the right track. Again, you should look into guards. instance Enum Nat where toEnum n | n <= 0 = Z | otherwise = ... -- do what with n? fromEnum Z = 0 fromEnum (S n) = 1 + fromEnum n You are on the right track. -- Deniz Dogan