base- Basic librariesSource codeContentsIndex
Functors: uniform action over a parameterized type, generalizing the map function on lists.
class Functor f where
fmap :: (a -> b) -> f a -> f b
(<$) :: a -> f b -> f a
(<$>) :: Functor f => (a -> b) -> f a -> f b
class Functor f whereSource

The Functor class is used for types that can be mapped over. Instances of Functor should satisfy the following laws:

 fmap id  ==  id
 fmap (f . g)  ==  fmap f . fmap g

The instances of Functor for lists, Data.Maybe.Maybe and System.IO.IO defined in the Prelude satisfy these laws.

fmap :: (a -> b) -> f a -> f bSource
(<$) :: a -> f b -> f aSource
Replace all locations in the input with the same value. The default definition is fmap . const, but this may be overridden with a more efficient version.
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(<$>) :: Functor f => (a -> b) -> f a -> f bSource
An infix synonym for fmap.
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