Functor

Functor class (base)

import Control.Monad

The Functor class is defined like this:

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

All instances of Functor should obey:

fmap id = id
fmap (p . q) = (fmap p) . (fmap q)

More reading

• The functor design pattern