base-4.3.1.0: Basic libraries

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 where

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 b

(<$) :: a -> f b -> f a

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 [::] |
Functor Maybe |
Functor ReadP |
Functor ReadPrec |
Functor STM |
Functor ZipList |
Functor Id |
Functor ((->) r) |
Functor (Either a) |
Functor ((,) a) |
Functor (ST s) |
Ix i => Functor (Array i) |
Monad m => Functor (WrappedMonad m) |
Functor (Const m) |
Functor (StateR s) |
Functor (StateL s) |
Functor (ST s) |
Arrow a => Functor (WrappedArrow a b) |

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

An infix synonym for `fmap`.