code: function (arg) {
    if (arg instanceof Array) {
      if (arg.length === 0) return ok.call(this);
      if (arg.length === 1) return ok.call(this, arg[0]);
      if (arg.length >= 2) {
        var head = arg[0];
        var tail = arg.slice(1);
        return ok.call(this, head, tail);
      }
    }
    if (arg instanceof Object) {
      if ("x" in arg && "y" in arg) {
        return ok.call(this, arg.x, arg.y);
      }
    }
    if (typeof arg === "number") {
      return ok.call(this);
    }
  }
docs: Handwritten fn --------------