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PGF exports the public, stable API. PGF.Internal exports additional things needed in the GF compiler & shell, including the nonstardard version of Data.Binary.
21 lines
785 B
Haskell
21 lines
785 B
Haskell
-- | Basic utilities
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module PGF.Utilities where
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import Data.Set(empty,member,insert)
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-- | Like 'Data.List.nub', but O(n log n) instead of O(n^2), since it uses a set to lookup previous things.
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-- The result list is stable (the elements are returned in the order they occur), and lazy.
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-- Requires that the list elements can be compared by Ord.
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-- Code ruthlessly taken from <http://hpaste.org/54411>
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nub' :: Ord a => [a] -> [a]
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nub' = loop empty
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where loop _ [] = []
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loop seen (x : xs)
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| member x seen = loop seen xs
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| otherwise = x : loop (insert x seen) xs
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-- | Replace all occurences of an element by another element.
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replace :: Eq a => a -> a -> [a] -> [a]
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replace x y = map (\z -> if z == x then y else z)
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