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Add a difference binding.

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This commit is contained in:
Rob Rix 2015-12-14 17:07:07 -05:00
parent 92a28ad38a
commit 8819f02306
1 changed files with 5 additions and 0 deletions
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5
src/OrderedMap.hs
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@ -10,6 +10,7 @@ module OrderedMap (
, union
, unions
, intersectionWith
, difference
) where
data OrderedMap key value = OrderedMap { toList :: [(key, value)] }
@ -46,3 +47,7 @@ unions = foldl union empty
intersectionWith :: Eq key => (a -> b -> c) -> OrderedMap key a -> OrderedMap key b -> OrderedMap key c
intersectionWith combine (OrderedMap a) (OrderedMap b) = OrderedMap $ a >>= (\ (key, value) -> maybe [] (pure . ((,) key) . combine value) $ Prelude.lookup key b)
difference :: Eq key => OrderedMap key a -> OrderedMap key b -> OrderedMap key a
difference (OrderedMap a) (OrderedMap b) = OrderedMap $ filter (not . (`elem` extant) . fst) a
where extant = fst <$> b