Semigroup

Keypoints:

closed + associative

foldMap is the same as .map().reduce()

Reader Functor

Keypoints:

Reader: Similar idea to Dependency injection

Endo Functor

Keypoints:

Endo: Same input and output types

contramap: transform the input before it passing to the function

contramap

Keypoints:

contramap: apply transform function on input arguements

Reducer

Keypoints:

reducer: Modelling the reducer pattern

Reducer, Endo

Keypoints:

Endo + Fn = Reducer:

// (acc, a) -> acc
// (a, acc) -> acc
// a -> acc -> acc
// a -> (acc -> acc)
// a -> Endo(acc -> acc)
// Fn(a -> Endo(acc -> acc))