Functor
From HaskellWiki
(Difference between revisions)
(Main article in category Functor) |
Artyom Kazak (Talk | contribs) m (fix broken link) |
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− | {{Standard class|Functor|module= | + | {{Standard class|Functor|module=Data.Functor|module-doc=Data-Functor|package=base}} |
The '''Functor''' class is defined like this: | The '''Functor''' class is defined like this: | ||
class Functor f where | class Functor f where | ||
fmap :: (a -> b) -> f a -> f b | fmap :: (a -> b) -> f a -> f b | ||
+ | |||
+ | It is available in the Prelude, but defined in Data.Functor. | ||
All instances of Functor should obey: | All instances of Functor should obey: | ||
− | fmap id = id | + | fmap id = id |
fmap (p . q) = (fmap p) . (fmap q) | fmap (p . q) = (fmap p) . (fmap q) | ||
+ | |||
+ | |||
+ | == More reading == | ||
+ | |||
+ | * [http://www.haskellforall.com/2012/09/the-functor-design-pattern.html The functor design pattern] | ||
+ | |||
+ | |||
[[Category:Functor|*]] | [[Category:Functor|*]] |
Latest revision as of 21:14, 13 October 2014
import Data.Functor |
The Functor class is defined like this:
class Functor f where fmap :: (a -> b) -> f a -> f b
It is available in the Prelude, but defined in Data.Functor.
All instances of Functor should obey:
fmap id = id fmap (p . q) = (fmap p) . (fmap q)