Re: [Haskell-beginners] Enum for natural numbers

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Datum: Sun, 20 Dec 2009 21:28:21 +0100 Von: Daniel Fischer An: beginners@haskell.org Betreff: Re: [Haskell-beginners] Enum for natural numbers

Am Sonntag 20 Dezember 2009 21:06:36 schrieb kane96@gmx.de:

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So,

toEnum n     | n < 0 = Z toEnum 0 = Z toEnum n = ?    -- here, we know n > 0

fromEnum should be the correspondnece the other way round, so

fromEnum Z = 0 fromEnum (S p) = ?      -- which Int corresponds to the successor of p?

what is P?

Any element of Nat (p for Peano).

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Now I read some short textes about it and think I know more or less what

I

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have to do for the exercise. But I don't know really how. Do you know any examples for it, how it normally looks like?

Deniz Dogan posted a few links to recursion earlier today, if you look at them, you should get the general idea. As a further example,

replicate :: Int -> a -> [a] replicate n x | n <= 0 = [] | otherwise = x:replicate (n-1) x

may help.

my problem is that I don't know how to use Enum correctly and didn't find any helpfull example

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