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Set Unions – add light weight pointer equality check #1157

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Set Unions – add light weight pointer equality check #1157

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3 changes: 2 additions & 1 deletion containers/src/Data/Set/Internal.hs
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Expand Up @@ -831,7 +831,8 @@ unions = Foldable.foldl' union empty
-- | \(O\bigl(m \log\bigl(\frac{n}{m}+1\bigr)\bigr), \; 0 < m \leq n\). The union of two sets, preferring the first set when
-- equal elements are encountered.
union :: Ord a => Set a -> Set a -> Set a
union t1 Tip = t1
union t1 t2 | t1 `ptrEq` t2 = t1
union t1 Tip = t1
union t1 (Bin 1 x _ _) = insertR x t1
union (Bin 1 x _ _) t2 = insert x t2
union Tip t2 = t2
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