In short, typeclass is just like interface, so it's not so hard to understand.

Let's see some code about Maybe functor, functor has a special map function:

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

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

Functor is a typeclass.
Applicative Functor extends Functor.
Monad extends Applicative.

class Applicative m => Monad m where
    return :: a -> m a
    (>>=) :: m a -> (a -> m b) -> m b

And another one Monoid is a math concept. It's a typeclass too.

They are all typeclasses.

ref

Functor、Applicative 和 Monad(Chinese)

Learn You a Haskell for Great Good!

Book Notes: Learn You a Haskell for Great Good!

Nested Software ・ Dec 4 '18 ・ 19 min read

#haskell #functional #monad #javascript