Re: [Haskell-beginners] Enum for natural numbers

Am Montag 21 Dezember 2009 10:56:06 schrieb kane96@gmx.de:

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)

Note that many frown upon (n+k)-patterns and they may be removed from the language in future. Use guards: toEnum n | condition1 = rhs1 | condition2 = rhs2

        fromEnum Z = 0         fromEnum (S n) = 1 + fromEnum n