33 lines
849 B
Haskell
33 lines
849 B
Haskell
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module Main where
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import Data.List
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import Test.QuickCheck
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-- Sorting twice changes nothing
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prop_idempotency :: Ord a => [a] -> Bool
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prop_idempotency xs = qsort xs == qsort (qsort xs)
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-- Sorting doesn't change the length
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prop_len :: Ord a => [a] -> Bool
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prop_len xs = length xs == length (qsort xs)
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-- Sorted result is a permutation of input
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prop_perm :: Ord a => [a] -> Bool
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prop_perm xs = (qsort xs) `elem` (permutations xs)
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-- Sorting produces sorted list
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prop_sort :: Ord a => [a] -> Bool
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prop_sort = isSorted . qsort
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where
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isSorted :: Ord a => [a] -> Bool
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isSorted [] = True
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isSorted [x] = True
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isSorted (x:y:zs) = (x <= y) && isSorted (y:zs)
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qsort :: Ord a => [a] -> [a]
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qsort [] = []
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qsort (p:xs) = (qsort lesser) ++ p:(qsort greater)
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where
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lesser = filter (< p) xs
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greater = filter (>= p) xs
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