Use Data.Ord.Down

We used to use our own `Down` newtype because the one in `Data.Ord`
had a somewhat lousy `Ord` instance. That has since been corrected, so
we can just do what everyone else does.

Author: treeowl

CHANGELOG.md

@@ -1,5 +1,10 @@
 # Revision history for pqueue
 
+## 1.5.0
+
+  * Remove `Data.PQueue.Internals.Down.Down`. Use the usual `Data.Ord.Down`
+    instead.
+
 ## 1.4.3.0 -- 2022-10-30
 
   * Add instances for [indexed-traversable](https://hackage.haskell.org/package/indexed-traversable).

src/BinomialQueue/Max.hs

@@ -98,7 +98,8 @@ import Data.Semigroup (Semigroup((<>)))
 import qualified Data.List as List
 
 import qualified BinomialQueue.Min as MinQ
-import Data.PQueue.Internals.Down
+import Data.PQueue.Internals.Down (getDown)
+import Data.Ord (Down (..))
 
 #ifdef __GLASGOW_HASKELL__
 import GHC.Exts (build)
@@ -115,7 +116,7 @@ findMax = fromMaybe (error "Error: findMax called on empty queue") . getMax
 
 -- | \(O(1)\). The top (maximum) element of the queue, if there is one.
 getMax :: Ord a => MaxQueue a -> Maybe a
-getMax (MaxQueue q) = unDown <$> MinQ.getMin q
+getMax (MaxQueue q) = getDown <$> MinQ.getMin q
 
 -- | \(O(\log n)\). Deletes the maximum element. If the queue is empty, does nothing.
 deleteMax :: Ord a => MaxQueue a -> MaxQueue a
@@ -142,19 +143,19 @@ q !! n = (List.!!) (toDescList q) n
 -- | 'takeWhile', applied to a predicate @p@ and a queue @queue@, returns the
 -- longest prefix (possibly empty) of @queue@ of elements that satisfy @p@.
 takeWhile :: Ord a => (a -> Bool) -> MaxQueue a -> [a]
-takeWhile p = fmap unDown . MinQ.takeWhile (p . unDown) . unMaxQueue
+takeWhile p = fmap getDown . MinQ.takeWhile (p . getDown) . unMaxQueue
 
 -- | 'dropWhile' @p queue@ returns the queue remaining after 'takeWhile' @p queue@.
 dropWhile :: Ord a => (a -> Bool) -> MaxQueue a -> MaxQueue a
-dropWhile p = MaxQueue . MinQ.dropWhile (p . unDown) . unMaxQueue
+dropWhile p = MaxQueue . MinQ.dropWhile (p . getDown) . unMaxQueue
 
 -- | 'span', applied to a predicate @p@ and a queue @queue@, returns a tuple where
 -- first element is longest prefix (possibly empty) of @queue@ of elements that
 -- satisfy @p@ and second element is the remainder of the queue.
 span :: Ord a => (a -> Bool) -> MaxQueue a -> ([a], MaxQueue a)
 span p (MaxQueue queue)
-  | (front, rear) <- MinQ.span (p . unDown) queue
-  = (fmap unDown front, MaxQueue rear)
+  | (front, rear) <- MinQ.span (p . getDown) queue
+  = (fmap getDown front, MaxQueue rear)
 
 -- | 'break', applied to a predicate @p@ and a queue @queue@, returns a tuple where
 -- first element is longest prefix (possibly empty) of @queue@ of elements that
@@ -177,19 +178,19 @@ drop n (MaxQueue queue) = MaxQueue (MinQ.drop n queue)
 splitAt :: Ord a => Int -> MaxQueue a -> ([a], MaxQueue a)
 splitAt n (MaxQueue queue)
   | (l, r) <- MinQ.splitAt n queue
-  = (fmap unDown l, MaxQueue r)
+  = (fmap getDown l, MaxQueue r)
 
 -- | \(O(n)\). Returns the queue with all elements not satisfying @p@ removed.
 filter :: Ord a => (a -> Bool) -> MaxQueue a -> MaxQueue a
-filter p = MaxQueue . MinQ.filter (p . unDown) . unMaxQueue
+filter p = MaxQueue . MinQ.filter (p . getDown) . unMaxQueue
 
 -- | \(O(n)\). Returns a pair where the first queue contains all elements satisfying @p@, and the second queue
 -- contains all elements not satisfying @p@.
 partition :: Ord a => (a -> Bool) -> MaxQueue a -> (MaxQueue a, MaxQueue a)
 partition p = go . unMaxQueue
   where
     go queue
-      | (l, r) <- MinQ.partition (p . unDown) queue
+      | (l, r) <- MinQ.partition (p . getDown) queue
       = (MaxQueue l, MaxQueue r)
 
 -- | \(O(n)\). Creates a new priority queue containing the images of the elements of this queue.
@@ -202,13 +203,13 @@ map f = MaxQueue . MinQ.map (fmap f) . unMaxQueue
 --
 -- If the order of the elements is irrelevant, consider using 'toListU'.
 toList :: Ord a => MaxQueue a -> [a]
-toList = fmap unDown . MinQ.toAscList . unMaxQueue
+toList = fmap getDown . MinQ.toAscList . unMaxQueue
 
 toAscList :: Ord a => MaxQueue a -> [a]
-toAscList = fmap unDown . MinQ.toDescList . unMaxQueue
+toAscList = fmap getDown . MinQ.toDescList . unMaxQueue
 
 toDescList :: Ord a => MaxQueue a -> [a]
-toDescList = fmap unDown . MinQ.toAscList . unMaxQueue
+toDescList = fmap getDown . MinQ.toAscList . unMaxQueue
 
 -- | \(O(n \log n)\). Performs a right fold on the elements of a priority queue in descending order.
 foldrDesc :: Ord a => (a -> b -> b) -> b -> MaxQueue a -> b
@@ -245,7 +246,7 @@ elemsU = toListU
 
 -- | Convert to a list in an arbitrary order.
 toListU :: MaxQueue a -> [a]
-toListU = fmap unDown . MinQ.toListU . unMaxQueue
+toListU = fmap getDown . MinQ.toListU . unMaxQueue
 
 -- | Get the number of elements in a 'MaxQueue'.
 size :: MaxQueue a -> Int
@@ -255,7 +256,7 @@ empty :: MaxQueue a
 empty = MaxQueue MinQ.empty
 
 foldMapU :: Monoid m => (a -> m) -> MaxQueue a -> m
-foldMapU f = MinQ.foldMapU (f . unDown) . unMaxQueue
+foldMapU f = MinQ.foldMapU (f . getDown) . unMaxQueue
 
 seqSpine :: MaxQueue a -> b -> b
 seqSpine = MinQ.seqSpine . unMaxQueue
@@ -267,7 +268,7 @@ foldlU' :: (b -> a -> b) -> b -> MaxQueue a -> b
 foldlU' f b = MinQ.foldlU' (\acc (Down a) -> f acc a) b . unMaxQueue
 
 foldrU :: (a -> b -> b) -> b -> MaxQueue a -> b
-foldrU c n = MinQ.foldrU (c . unDown) n . unMaxQueue
+foldrU c n = MinQ.foldrU (c . getDown) n . unMaxQueue
 
 null :: MaxQueue a -> Bool
 null = MinQ.null . unMaxQueue
@@ -276,13 +277,13 @@ singleton :: a -> MaxQueue a
 singleton = MaxQueue . MinQ.singleton . Down
 
 mapMaybe :: Ord b => (a -> Maybe b) -> MaxQueue a -> MaxQueue b
-mapMaybe f = MaxQueue . MinQ.mapMaybe (fmap Down . f . unDown) . unMaxQueue
+mapMaybe f = MaxQueue . MinQ.mapMaybe (fmap Down . f . getDown) . unMaxQueue
 
 insert :: Ord a => a -> MaxQueue a -> MaxQueue a
 insert a (MaxQueue q) = MaxQueue (MinQ.insert (Down a) q)
 
 mapEither :: (Ord b, Ord c) => (a -> Either b c) -> MaxQueue a -> (MaxQueue b, MaxQueue c)
-mapEither f (MaxQueue q) = case MinQ.mapEither (bimap Down Down . f . unDown) q of
+mapEither f (MaxQueue q) = case MinQ.mapEither (bimap Down Down . f . getDown) q of
   (l, r) -> (MaxQueue l, MaxQueue r)
 
 union :: Ord a => MaxQueue a -> MaxQueue a -> MaxQueue a

src/Data/PQueue/Internals/Down.hs

@@ -1,37 +1,11 @@
 {-# LANGUAGE CPP #-}
-{-# LANGUAGE BangPatterns #-}
 
-module Data.PQueue.Internals.Down where
+module Data.PQueue.Internals.Down
+  ( getDown
+  ) where
+import Data.Ord (Down (..))
 
-import Control.DeepSeq (NFData(rnf))
-import Data.Foldable (Foldable (..))
-
-#if __GLASGOW_HASKELL__
-import Data.Data (Data)
-#endif
-
-newtype Down a = Down { unDown :: a }
-#if __GLASGOW_HASKELL__
-  deriving (Eq, Data)
-#else
-  deriving (Eq)
+#if !MIN_VERSION_base(4,14,0)
+getDown :: Down a -> a
+getDown (Down a) = a
 #endif
-
-instance NFData a => NFData (Down a) where
-  rnf (Down a) = rnf a
-
-instance Ord a => Ord (Down a) where
-  Down a `compare` Down b = b `compare` a
-  Down a <= Down b = b <= a
-  Down a >= Down b = b >= a
-  Down a < Down b = b < a
-  Down a > Down b = b > a
-
-instance Functor Down where
-  fmap f (Down a) = Down (f a)
-
-instance Foldable Down where
-  foldr f z (Down a) = a `f` z
-  foldl f z (Down a) = z `f` a
-  foldr' f !z (Down a) = a `f` z
-  foldl' f !z (Down a) = z `f` a

src/Data/PQueue/Max.hs

@@ -94,7 +94,8 @@ import Data.Foldable (foldl')
 
 import qualified Data.PQueue.Min as Min
 import qualified Data.PQueue.Prio.Max.Internals as Prio
-import Data.PQueue.Internals.Down (Down(..))
+import Data.PQueue.Internals.Down (getDown)
+import Data.Ord (Down(..))
 
 import Prelude hiding (null, map, take, drop, takeWhile, dropWhile, splitAt, span, break, (!!), filter)
 
@@ -171,7 +172,7 @@ findMax = fromMaybe (error "Error: findMax called on empty queue") . getMax
 
 -- | \(O(1)\). The top (maximum) element of the queue, if there is one.
 getMax :: MaxQueue a -> Maybe a
-getMax (MaxQ q) = unDown <$> Min.getMin q
+getMax (MaxQ q) = getDown <$> Min.getMin q
 
 -- | \(O(\log n)\). Deletes the maximum element of the queue. Does nothing on an empty queue.
 deleteMax :: Ord a => MaxQueue a -> MaxQueue a
@@ -210,7 +211,7 @@ unions qs = MaxQ (Min.unions [q | MaxQ q <- qs])
 
 -- | \(O(k \log n)\)/. Returns the @(k+1)@th largest element of the queue.
 (!!) :: Ord a => MaxQueue a -> Int -> a
-MaxQ q !! n = unDown ((Min.!!) q n)
+MaxQ q !! n = getDown ((Min.!!) q n)
 
 {-# INLINE take #-}
 -- | \(O(k \log n)\)/. Returns the list of the @k@ largest elements of the queue, in descending order, or
@@ -224,25 +225,25 @@ drop k (MaxQ q) = MaxQ (Min.drop k q)
 
 -- | \(O(k \log n)\)/. Equivalent to @(take k queue, drop k queue)@.
 splitAt :: Ord a => Int -> MaxQueue a -> ([a], MaxQueue a)
-splitAt k (MaxQ q) = (fmap unDown xs, MaxQ q') where
+splitAt k (MaxQ q) = (fmap getDown xs, MaxQ q') where
   (xs, q') = Min.splitAt k q
 
 -- | 'takeWhile', applied to a predicate @p@ and a queue @queue@, returns the
 -- longest prefix (possibly empty) of @queue@ of elements that satisfy @p@.
 takeWhile :: Ord a => (a -> Bool) -> MaxQueue a -> [a]
-takeWhile p (MaxQ q) = fmap unDown (Min.takeWhile (p . unDown) q)
+takeWhile p (MaxQ q) = fmap getDown (Min.takeWhile (p . getDown) q)
 
 -- | 'dropWhile' @p queue@ returns the queue remaining after 'takeWhile' @p queue@.
 dropWhile :: Ord a => (a -> Bool) -> MaxQueue a -> MaxQueue a
-dropWhile p (MaxQ q) = MaxQ (Min.dropWhile (p . unDown) q)
+dropWhile p (MaxQ q) = MaxQ (Min.dropWhile (p . getDown) q)
 
 -- | 'span', applied to a predicate @p@ and a queue @queue@, returns a tuple where
 -- first element is longest prefix (possibly empty) of @queue@ of elements that
 -- satisfy @p@ and second element is the remainder of the queue.
 --
 span :: Ord a => (a -> Bool) -> MaxQueue a -> ([a], MaxQueue a)
-span p (MaxQ q) = (fmap unDown xs, MaxQ q') where
-  (xs, q') = Min.span (p . unDown) q
+span p (MaxQ q) = (fmap getDown xs, MaxQ q') where
+  (xs, q') = Min.span (p . getDown) q
 
 -- | 'break', applied to a predicate @p@ and a queue @queue@, returns a tuple where
 -- first element is longest prefix (possibly empty) of @queue@ of elements that
@@ -252,13 +253,13 @@ break p = span (not . p)
 
 -- | \(O(n)\). Returns a queue of those elements which satisfy the predicate.
 filter :: Ord a => (a -> Bool) -> MaxQueue a -> MaxQueue a
-filter p (MaxQ q) = MaxQ (Min.filter (p . unDown) q)
+filter p (MaxQ q) = MaxQ (Min.filter (p . getDown) q)
 
 -- | \(O(n)\). Returns a pair of queues, where the left queue contains those elements that satisfy the predicate,
 -- and the right queue contains those that do not.
 partition :: Ord a => (a -> Bool) -> MaxQueue a -> (MaxQueue a, MaxQueue a)
 partition p (MaxQ q) = (MaxQ q0, MaxQ q1)
-  where  (q0, q1) = Min.partition (p . unDown) q
+  where  (q0, q1) = Min.partition (p . getDown) q
 
 -- | \(O(n)\). Maps a function over the elements of the queue, and collects the 'Just' values.
 mapMaybe :: Ord b => (a -> Maybe b) -> MaxQueue a -> MaxQueue b
@@ -267,7 +268,7 @@ mapMaybe f (MaxQ q) = MaxQ (Min.mapMaybe (\(Down x) -> Down <$> f x) q)
 -- | \(O(n)\). Maps a function over the elements of the queue, and separates the 'Left' and 'Right' values.
 mapEither :: (Ord b, Ord c) => (a -> Either b c) -> MaxQueue a -> (MaxQueue b, MaxQueue c)
 mapEither f (MaxQ q) = (MaxQ q0, MaxQ q1)
-  where  (q0, q1) = Min.mapEither (either (Left . Down) (Right . Down) . f . unDown) q
+  where  (q0, q1) = Min.mapEither (either (Left . Down) (Right . Down) . f . getDown) q
 
 -- | \(O(n)\). Creates a new priority queue containing the images of the elements of this queue.
 -- Equivalent to @'fromList' . 'Data.List.map' f . toList@.
@@ -287,7 +288,7 @@ foldrU f z (MaxQ q) = Min.foldrU (flip (foldr f)) z q
 --
 -- @since 1.4.2
 foldMapU :: Monoid m => (a -> m) -> MaxQueue a -> m
-foldMapU f (MaxQ q) = Min.foldMapU (f . unDown) q
+foldMapU f (MaxQ q) = Min.foldMapU (f . getDown) q
 
 -- | \(O(n)\). Unordered left fold on a priority queue. This is rarely
 -- what you want; 'foldrU' and 'foldlU'' are more likely to perform
@@ -309,7 +310,7 @@ elemsU = toListU
 {-# INLINE toListU #-}
 -- | \(O(n)\). Returns a list of the elements of the priority queue, in no particular order.
 toListU :: MaxQueue a -> [a]
-toListU (MaxQ q) = fmap unDown (Min.toListU q)
+toListU (MaxQ q) = fmap getDown (Min.toListU q)
 
 -- | \(O(n \log n)\). Performs a right-fold on the elements of a priority queue in ascending order.
 -- @'foldrAsc' f z q == 'foldlDesc' (flip f) z q@.
@@ -346,7 +347,7 @@ toDescList q = build (\c nil -> foldrDesc c nil q)
 --
 -- If the order of the elements is irrelevant, consider using 'toListU'.
 toList :: Ord a => MaxQueue a -> [a]
-toList (MaxQ q) = fmap unDown (Min.toList q)
+toList (MaxQ q) = fmap getDown (Min.toList q)
 
 {-# INLINE fromAscList #-}
 -- | \(O(n)\). Constructs a priority queue from an ascending list. /Warning/: Does not check the precondition.