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diff --git a/src/runtime/haskell/PGF/Utilities.hs b/src/runtime/haskell/PGF/Utilities.hs
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+-- | Basic utilities
+module PGF.Utilities where
+import Data.Set(empty,member,insert)
+
+
+-- | Like '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)