function a(k, x1, x2, x3, x4, x5) {
  function b() {
    k -= 1;
    return a(k, b, x1, x2, x3, x4);
  }
  return (k > 0) ? b() : x4() + x5();
}

// this uses lambda wrappers around the numeric arguments
function x(n) {
  return function () {
    return n;
  };
}
alert(a(10, x(1), x(-1), x(-1), x(1), x(0)));