category-extras-0.53.6: Various modules and constructs inspired by category theoryContentsIndex
Portabilitynon-portable (functional-dependencies)
MaintainerEdward Kmett <>
A more categorical definition of Functor than endofunctors in the category Hask
class (Category r, Category t) => PFunctor p r t | p r -> t, p t -> r where
first :: r a b -> t (p a c) (p b c)
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first' :: Bifunctor p r s t => r a b -> t (p a c) (p b c)
class (Category s, Category t) => QFunctor q s t | q s -> t, q t -> s where
second :: s a b -> t (q c a) (q c b)
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second' :: Bifunctor p r s t => s a b -> t (p c a) (p c b)
class (PFunctor p r t, QFunctor p s t) => Bifunctor p r s t | p r -> s t, p s -> r t, p t -> r s where
bimap :: r a b -> s c d -> t (p a c) (p b d)
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dimap :: Bifunctor f (Dual k) k k => k b a -> k c d -> k (f a c) (f b d)
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