functional javascript

<html><body><pre><script>

document.writeln('Hello, world!');

// functional programming test
let factorial = function (x) {
  let fact_iter = function fact_iter (x, acc) {
    if (x === 0) {
      return acc }
    else {
      return fact_iter (x-1, acc*x) }}
  return fact_iter (x, 1) }

document.writeln("5! = " + factorial(5));
document.writeln("10! = " + factorial(10));

// no tail optimization, so: trampoline version.
let safer_factorial = function (x) {

  // build the trampoline

  let trampoline_factorial = function trampoline_factorial(x, acc) {
    if (x === 0) {
      return {next: null, result: acc}}
    else {
      return {next: function () {return trampoline_factorial(x-1, x*acc)}}}}

  // wheee!!!

  var state = trampoline_factorial(x, 1);

  while (state.next) {
    state = state.next()}

  return state.result }

document.writeln("7! = " + safer_factorial(7));

</script></pre></body></html>