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