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Add a Monoid instance for Join.

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This commit is contained in:
Rob Rix 2016-02-28 21:18:03 -05:00
parent ea87105b4b
commit e33014ef27
1 changed files with 4 additions and 0 deletions
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4
src/Data/Bifunctor/Join.hs
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@ -6,3 +6,7 @@ newtype Join a = Join { runJoin :: (a, a) }
instance Applicative Join where
pure a = Join (a, a)
Join (f, g) <*> Join (a, b) = Join (f a, g b)
instance Monoid a => Monoid (Join a) where
mempty = pure mempty
mappend a b = pure mappend <*> a <*> b