52 lines
1.1 KiB
Haskell
52 lines
1.1 KiB
Haskell
module LibraryFunctions where
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-- 1
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sum :: (Foldable t, Num a) => t a -> a
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sum = foldr (+) 0
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-- 2
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product :: (Foldable t, Num a) => t a -> a
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product = foldr (*) 0
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-- 3
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elem :: (Foldable t, Eq a) => a -> t a -> Bool
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elem needle = foldr (\x b -> b || (needle == x)) False
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-- 4
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minimum :: (Foldable t, Ord a) => t a -> Maybe a
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minimum = foldr f Nothing
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where f x Nothing = Just x
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f x (Just y)
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| x > y = Just x
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| otherwise = Just y
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-- 5
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maximum :: (Foldable t, Ord a) => t a -> Maybe a
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maximum = foldr f Nothing
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where f x Nothing = Just x
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f x (Just y)
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| x < y = Just x
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| otherwise = Just y
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-- 6
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null :: (Foldable t) => t a -> Bool
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null f = LibraryFunctions.length f == 0
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-- 7
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length :: (Foldable t) => t a -> Int
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length = foldr (\_ l -> l + 1) 0
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-- 8
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toList :: (Foldable t) => t a -> [a]
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toList = foldr (:) []
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-- 9
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-- | Combine the elements of a structure using a monoid.
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--
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fold :: (Foldable t, Monoid m) => t m -> m
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fold = LibraryFunctions.foldMap id
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-- 10
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foldMap :: (Foldable t, Monoid m) => (a -> m) -> t a -> m
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foldMap f t = foldr (\x m -> mappend (f x) m) mempty t
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