Create NonEmptySet type

containers-tests/tests/set-properties.hs

@@ -238,15 +238,15 @@ mkArb step n
      p <- step
      q <- step
      if dir
-       then return (Bin 2 q (singleton p) Tip)
-       else return (Bin 2 p Tip (singleton q))
+       then return (NE $ Bin 2 q (singleton p) Tip)
+       else return (NE $ Bin 2 p Tip (singleton q))
   | otherwise = do
       -- This assumes a balance factor of delta = 3
       let upper = (3*(n - 1)) `quot` 4
       let lower = (n + 2) `quot` 4
       ln <- liftGen $ choose (lower, upper)
       let rn = n - ln - 1
-      liftM3 (\lt x rt -> Bin n x lt rt) (mkArb step ln) step (mkArb step rn)
+      liftM3 (\lt x rt -> NE $ Bin n x lt rt) (mkArb step ln) step (mkArb step rn)
 
 -- | Given a strictly increasing list of elements, produce an arbitrarily
 -- shaped set with exactly those elements.

containers/src/Data/Map/Internal.hs

@@ -1929,7 +1929,7 @@ difference t1 (NE (Bin _ k _ l2 r2)) = case split k t1 of
 withoutKeys :: Ord k => Map k a -> Set k -> Map k a
 withoutKeys Tip _ = Tip
 withoutKeys m Set.Tip = m
-withoutKeys m (Set.Bin _ k ls rs) = case splitMember k m of
+withoutKeys m (Set.NE (Set.Bin _ k ls rs)) = case splitMember k m of
   (lm, b, rm)
      | not b && lm' `ptrEq` lm && rm' `ptrEq` rm -> m
      | otherwise -> link2 lm' rm'
@@ -3356,7 +3356,8 @@ assocs m
 
 keysSet :: Map k a -> Set.Set k
 keysSet Tip = Set.Tip
-keysSet (NE (Bin sz kx _ l r)) = Set.Bin sz kx (keysSet l) (keysSet r)
+keysSet (NE (Bin sz kx _ l r)) = Set.NE $
+  Set.Bin sz kx (keysSet l) (keysSet r)
 
 -- | /O(n)/. Build a map from a set of keys and a function which for each key
 -- computes its value.
@@ -3366,7 +3367,7 @@ keysSet (NE (Bin sz kx _ l r)) = Set.Bin sz kx (keysSet l) (keysSet r)
 
 fromSet :: (k -> a) -> Set.Set k -> Map k a
 fromSet _ Set.Tip = Tip
-fromSet f (Set.Bin sz x l r) = NE $ Bin sz x (f x) (fromSet f l) (fromSet f r)
+fromSet f (Set.NE (Set.Bin sz x l r)) = NE $ Bin sz x (f x) (fromSet f l) (fromSet f r)
 
 {--------------------------------------------------------------------
   Lists

containers/src/Data/Map/Strict/Internal.hs

@@ -1469,7 +1469,8 @@ mapKeysWith c f = fromListWith c . foldrWithKey (\k x xs -> (f k, x) : xs) []
 
 fromSet :: (k -> a) -> Set.Set k -> Map k a
 fromSet _ Set.Tip = Tip
-fromSet f (Set.Bin sz x l r) = case f x of v -> v `seq` NE (Bin sz x v (fromSet f l) (fromSet f r))
+fromSet f (Set.NE (Set.Bin sz x l r)) = case f x of
+  v -> v `seq` NE (Bin sz x v (fromSet f l) (fromSet f r))
 
 {--------------------------------------------------------------------
   Lists

containers/src/Data/Set.hs

@@ -70,6 +70,7 @@ module Data.Set (
               Set          -- instance Eq,Ord,Show,Read,Data,Typeable
 #else
               Set(..)
+            , NonEmptySet(..)
 #endif
 
             -- * Construction