Functors

Question 1

give the implementation of the Functor typeclass

Answer 1

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

Question 2

what is the purpose of functors?

Answer 2

If a type is an instance of Functor, you can use fmap to apply a function to values in it. Another way of describing fmap is saying that it promotes functions to act on functorial values.

Question 3

give the 1st functor law

Answer 3

fmap id = id

Question 4

give the 2nd functor law

Answer 4

fmap (g . f) = fmap g . fmap f