As I said, it’s just an example.

For example

const sum= a => b => a + b;

First we are defining a function as a constant. How is it natural?

But even more, we couldn’t call the function as follow sum(1,2) cause it returns the definition of the function. It is mean to be parsed as an argument of a function, so we have a function that is coupled with another, it’s not safe to use everywhere and debugging is fun-for-the-family.