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5a ex11

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Aaro Koivukangas
2025-12-23 01:27:46 +02:00
parent 501d13ddb3
commit df26a99410
1 changed files with 9 additions and 2 deletions
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exercises/Set5a.hs
+9 -2
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@@ -271,10 +271,17 @@ data Nat = Zero | PlusOne Nat
deriving (Show,Eq) deriving (Show,Eq)
fromNat :: Nat -> Int fromNat :: Nat -> Int
fromNat n = todo fromNat n = case n of
PlusOne n -> 1 + fromNat n
Zero -> 0
toNat :: Int -> Maybe Nat toNat :: Int -> Maybe Nat
toNat z = todo toNat z = if z >= 0 then Just (toNat' z) else Nothing
where
toNat' :: Int -> Nat
toNat' z
| z>0 = PlusOne $ toNat' (z-1)
| z==0 = Zero
------------------------------------------------------------------------------ ------------------------------------------------------------------------------
-- Ex 12: While pleasingly simple in its definition, the Nat datatype is not -- Ex 12: While pleasingly simple in its definition, the Nat datatype is not