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Category cat => Monoid (Join cat a) #64

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Icelandjack opened this issue Sep 23, 2017 · 0 comments

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Icelandjack commented Sep 23, 2017 •

edited

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instance Category cat => Semigroup (Join cat a) where
  Join f <> Join g = Join (f . g)

instance Category cat => Monoid (Join cat a) where
  mempty  = Join id
  mappend = (<>)

This allows deriving Monoid (Kleisli m a a) and

newtype Endo a = Endo { appEndo :: Join (->) a }
  deriving 
    (Semigroup, Monoid)

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