Why does the kind matter? Both of your examples use type inference and polymorphism - the type 'a' is inferred when quux is used, the type for the second exampl

Why does the kind matter? Both of your examples use type inference and polymorphism - the type 'a' is inferred when quux is used, the type for the second example is inferred from the polymorphic types of (++) and `$`, and both allow to code more freely while in flux.