From a7b3ee033e3461b3682ebb3aff37e6d659321c74 Mon Sep 17 00:00:00 2001
From: Hans-Peter Deifel <hpd@hpdeifel.de>
Date: Fri, 8 Mar 2019 09:26:24 +0100
Subject: [PATCH] SumBag: Implement Foldable
---
src/Data/SumBag.hs | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
diff --git a/src/Data/SumBag.hs b/src/Data/SumBag.hs
index 12267b5..4a36612 100644
--- a/src/Data/SumBag.hs
+++ b/src/Data/SumBag.hs
@@ -13,6 +13,7 @@ module Data.SumBag
) where
import Prelude hiding (sum, min, elem)
+import Data.Foldable hiding (sum,elem)
import qualified Data.List.NonEmpty as NE
type SumBag a = Tree a
@@ -20,10 +21,26 @@ type SumBag a = Tree a
data Tree a = Leaf | Node (MetaData a) (Element a) (Tree a) (Tree a)
deriving (Show)
+type role Tree nominal
+
instance (Ord a, Eq a) => Eq (Tree a) where
x == y = toAscList x == toAscList y
-type role Tree nominal
+-- TODO There are a few functions from foldable that can be implemented way more
+-- efficiently.
+--
+-- Notably 'minimum' and 'maximum', but also explicit recursion instead of
+-- conversions to lists in a lot of cases.
+instance Foldable Tree where
+ foldMap f = foldMap f . toAscList
+ {-# INLINE foldMap #-}
+
+ fold = sum
+ {-# INLINE fold #-}
+
+ toList = toAscList
+ {-# INLINE toList #-}
+
data MetaData a = MetaData
{ nodeSize :: Int
@@ -81,7 +98,7 @@ delete a (Node _ e left right)
let (min, rest) = delmin right
in balance1 min left rest
-toAscList :: Ord a => SumBag a -> [a]
+toAscList :: SumBag a -> [a]
toAscList bag = helper bag []
where helper Leaf accu = accu
helper (Node _ e left right) accu =
--
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