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Remove the Monoid instance for App, as it’s unlawful.

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This commit is contained in:
Rob Rix 2018-03-21 17:26:32 -04:00
parent aab509cf63
commit 6a785e0b30
1 changed files with 0 additions and 7 deletions
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7
src/Data/Semigroup/App.hs
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@ -21,13 +21,6 @@ newtype App f a = App { runApp :: f a }
instance Applicative f => Semigroup (App f a) where
App a <> App b = App (a *> b)
-- $ Identity:
-- prop> \ a -> mempty <> a == (a :: App Maybe String)
-- prop> \ a -> a <> mempty == (a :: App Maybe String)
instance (Applicative f, Monoid a) => Monoid (App f a) where
mempty = App (pure mempty)
mappend = (<>)
-- | 'Semigroup' under '<*>' and '<>'.
newtype AppMerge f a = AppMerge { runAppMerge :: f a }