'use strict';

function test(...args) {
    args = Array.prototype.slice.call(args);

    let result = function (...args2) {
        return test.apply(test, args.concat(Array.prototype.slice.call(args2)));
    };

    result.toString = function () {
        return Array.prototype.slice.call(args).reduce((accum, item) => accum + item, 0);
    };

    return result;
}

console.log('SUM ' + test(1, 2, 3)(4, 5, 6)(7, 8, 9));