How come the definitions of “functor”, “applicative functor”, etc. don't mention the most important part? The laws. The definition of equational reasoning is a

How come the definitions of “functor”, “applicative functor”, etc. don't mention the most important part? The laws. The definition of equational reasoning is also very weak: > When an application is composed of expressions and devoid of side effects, truths about the system can be derived from the parts. Truths about any system can be derived from the parts. What equational reasoning gives you is the ability to study the parts in isolation from each other.