Re: [Haskell-beginners] Enum for natural numbers

2009/12/18 :

ahhh, ok, thanks so far. Here is how the output should looks like: *Main> toEnum (-1) :: Nat Z *Main> toEnum 0 :: Nat Z *Main> toEnum 1 :: Nat S Z *Main> fromEnum (S (S Z)) 2

the first three things work, but I don't know about the last one. Does anybody how it should work and what's the sense of it?

Looks right to me. "Z" means 0 (Zero), "S x" means "the Successor of x". So (S (S (S Z))) means "the successor of the successor of the successor of zero", which is 3.

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Datum: Fri, 18 Dec 2009 18:06:32 +0100 Von: Deniz Dogan An: kane96@gmx.de CC: beginners@haskell.org Betreff: Re: [Haskell-beginners] Enum for natural numbers

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2009/12/17  :

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Hi, I have data Nat = Z | S Nat deriving (Eq,Ord,Show)

toEnum should return Z for negative numbers. I did something like this but the problem is I don't know how to set "less than". I tried > and lt:

instance Enum Nat where    toEnum (gt 0) = S Z    toEnum (lt 1) = Z -- GRATIS für alle GMX-Mitglieder: Die maxdome Movie-FLAT! Jetzt freischalten unter http://portal.gmx.net/de/go/maxdome01 _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners

Fill in the gaps:

instance Enum Nat where     toEnum x | x <= 0 = ...              | otherwise = ...

-- Deniz Dogan

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-- Deniz Dogan