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Maybe is a PartialSemigroup under a Monoid.

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This commit is contained in:
Rob Rix 2016-03-05 01:00:11 -05:00
parent 4deabf496f
commit 63802d3137
1 changed files with 5 additions and 0 deletions
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src/Data/Adjoined.hs
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@ -32,3 +32,8 @@ instance PartialSemigroup a => Monoid (Adjoined a) where
instance PartialSemigroup Bool where
coalesce True = Just
coalesce False = const Nothing
instance Monoid a => PartialSemigroup (Maybe a) where
coalesce Nothing _ = Nothing
coalesce _ Nothing = Nothing
coalesce (Just a) (Just b) = Just (Just (a `mappend` b))