Functorial data types
Type constructors related to container & parameterized types
Important: type constructors not to be confused with arrows between objects
Functor as a kind of mapping that preserves structure
Functors must preserve identity arrows
Functors map objects but also arrows between them and therefore preserve structure
Functors must preserve composition
Functoriality in Haskell (Functor type class and `fmap`)
Functoriality & Lifting
Type constructors: mapping types to other types
Composition and identity preservation with functors left to the programmer in Haskell