In this case the point of the excercise is to help you learn how to format String data types in code, not to persuade you that american phone numbers are better. If you were developing software for a company someday in the future, you would need to be able to offer multiple formats for a phone number based off of the formatting style that the user prefers.

This is a Kata that I don't even remember when I solved, obviously I was either drowsy or just wasn't that familiar with programming back then

Haskell says partial application works.

Dicts are functions would be Scott encoding.

JavaScript just stands there and looks on uncomprehendingly, wondering where this went.