Functoriality

https://bartoszmilewski.com/2015/02/03/functoriality/

1. Category: The Essence of Composition

2. Types and Functions

3. Categories Great and Small

4. Kleisli Categories

5. Products and Coproducts

6. Simple Algebraic Data Types

7. Functors

8. Functoriality

9. Function Types

10. Natural Transformations