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Define a Monoid instance for Map.

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This commit is contained in:
Rob Rix 2018-03-07 12:26:32 -05:00
parent 303e55b403
commit f199e7fa73
1 changed files with 4 additions and 0 deletions
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src/Data/Map/Monoidal.hs
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@ -10,3 +10,7 @@ newtype Map key value = Map { unMap :: Map.Map key value }
instance (Ord key, Semigroup value) => Semigroup (Map key value) where
Map a <> Map b = Map (Map.unionWith (<>) a b)
instance (Ord key, Semigroup value) => Monoid (Map key value) where
mempty = Map Map.empty
mappend = (<>)