roam/20220316184243-functor.org

Functor

• Examples
  • Maybe

In Software Development, this refers to a parameterized data type that wraps a value in a context and provides a method for applying a function to the wrapped value, independent of the container type.

In Haskell, the function for applying a function to a value in a functor is fmap, also available as the infix operator <$>.

  fmap :: Functor f => (a -> b) -> f a -> f b

fmap in Haskell

Examples

Maybe

  instance Functor Maybe where
    fmap func (Just n) = Just (func n)
    fmap func Nothing = Nothing

Implementation of Functor for Maybe in Haskell