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Control.Functor | Portability | portable | Stability | experimental | Maintainer | zednenem@psualum.com |
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Description |
Functor composition, standard functors, and more.
Note: declares functor instance for ((,) a)
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Synopsis |
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Unary functors |
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Composition |
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newtype O f g a |
Functor composition.
(Note: Some compilers will let you write f `O` g rather than O f g;
we'll be doing so here for readability.)
Functor composition is associative, so f `O` (g `O` h) and (f `O` g) `O` h
are equivalent. The functions lComp and rComp convert between the two.
(Operationally, they are equivalent to id. Their only purpose is to affect
the type system.)
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lComp :: Functor f => O f (O g h) a -> O (O f g) h a |
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rComp :: Functor f => O (O f g) h a -> O f (O g h) a |
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Basic instances |
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Id |
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newtype Id a |
The identity functor (or a reasonable facsimile thereof).
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Unit |
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data Unit a |
The unit functor.
(Note: this is not the same as (). In fact, Unit is the
fixpoint of ().)
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Const |
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data Const t a |
Constant functors. Essentially the same as Unit, except that they also
carry a value.
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Binary functors |
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class Bifunctor f where |
A type constructor which takes two arguments and an associated map function.
Informally, Bifunctor f implies Functor (f a) with fmap = bimap id.
| | Methods | bimap :: (a -> c) -> (b -> d) -> f a b -> f c d |
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Trinary functors |
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class Trifunctor f where |
A type constructor which takes three arguments and an associated map function.
Informally, Trifunctor f implies Bifunctor (f a) with bimap = trimap id.
| | Methods | trimap :: (a -> a') -> (b -> b') -> (c -> c') -> f a b c -> f a' b' c' |
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Produced by Haddock version 0.6 |