Portability	portable
Stability	provisional
Maintainer	libraries@haskell.org

Data.Functor

Description

Functors: uniform action over a parameterized type, generalizing the map function on lists.

Synopsis

class Functor f where
- fmap :: (a -> b) -> f a -> f b
- (<$) :: a -> f b -> f a
(<$>) :: Functor f => (a -> b) -> f a -> f b

Documentation

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 satisfy these laws.

Methods

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.

Instances

Functor []

Functor IO

Functor STM

Functor Id

Functor ((->) r)

Functor (Either a)

Functor ((,) a)

Functor (ST s)

Ix i => Functor (Array i)

Functor (ST s)

Monad m => Functor (WrappedMonad m)

Functor (Const m)

Functor (StateR s)

Functor (StateL s)

Arrow a => Functor (WrappedArrow a b)

(<$>) :: Functor f => (a -> b) -> f a -> f bSource

An infix synonym for fmap .