Wisp vs Wisp's Idea of JavaScript vs real JavaScript

huh.js

// Wisp:

(fn sum
  "Return the sum of all arguments"
  {:version "1.0"}
  ([] 0)
  ([x] x)
  ([x y] (+ x y))
  ([x & more] (more.reduce (fn [x y] (+ x y)) x)))

// What Wisp's developers thinks good JavaScript looks like:

function sum(x, y) {
  switch (arguments.length) {
    case 0:
      return 0;
    case 1:
      return x;
    case 2:
      return x + y;
    
    default:
      var more = Array.prototype.slice.call(arguments, 1);
      return more.reduce(function(x, y) {
        return x + y;
      }, x);
  };
  return void(0);
};

// Real JavasScript:

function sum(x, y) {
  if(arguments.length < 1) return 0;

  return [].slice.call(arguments).reduce(function(x, y) {
      return x + y;
  });
};