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Comonad instance for (Lift f) #40

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Icelandjack opened this issue Oct 2, 2017 · 0 comments
Open

Comonad instance for (Lift f) #40

Icelandjack opened this issue Oct 2, 2017 · 0 comments

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@Icelandjack
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I can make a PR later if desired, but there should be a Comonad instance for Lift f

instance Comonad f => Comonad (Lift f) where
  extract :: Lift f a -> a
  extract (Pure a)   = a
  extract (Other fa) = extract fa

  extend :: (Lift f a -> b) -> (Lift f a -> Lift f b)
  extend f = \case
    Pure  a  -> Pure  $ f (Pure a)
    Other fa -> Other $ extend (f . Other) fa
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