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Functor

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(Main article in category Functor)
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{{Standard class|Functor|module=Control.Monad|module-doc=Control-Monad|package=base}}
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{{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
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 +
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
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  fmap id     = id
 
  fmap (p . q) = (fmap p) . (fmap q)
 
  fmap (p . q) = (fmap p) . (fmap q)
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== More reading ==
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* [http://www.haskellforall.com/2012/09/the-functor-design-pattern.html The functor design pattern]
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[[Category:Functor|*]]
 
[[Category:Functor|*]]

Latest revision as of 21:14, 13 October 2014

Functor class (base)
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)


[edit] More reading