streams.js

function nums(n = 1) {
  return { first: n, rest: () => nums(n + 1) };
}

nums().first;  // => 1

function take(stream, n) {
  if (n <= 0) return [];
  else {
    const { first, rest } = stream();
    return [first].concat(take(rest, n - 1));
  }
}

take(nums, 5);  // => [1, 2, 3, 4, 5]

function nth(stream, n) {
  if (n < 0) return null;
  const { first, rest } = stream();
  if (n === 0) return first;
  else return nth(rest, n - 1);
}

nth(nums, 100);  // => 101

function odds(n = 1) {
  return { first: n, rest: () => nums(n + 2) };
}

// function odds(n = 0) {
//   return { first: 2 * n + 1, rest: () => odds(n + 1) };
// }

take(odds, 5);  // => [1, 3, 5, 7, 9]

function squares(n = 0) {
  return { first: (n + 1) ** 2, rest: () => squares(n + 1) };
}

// function squares(n = 1) {
//   return { first: n * n, rest: () => squares(n + 1) };
// }

take(squares, 5);  // => [1, 4, 9, 16, 25]

function flipFlop(n = 0) {
  return { first: n, rest: () => flipFlop(n === 0 ? 1 : 0) };
}

// function flipFlop(n = 0) {
//   return { first: n % 2, rest: () => flipFlop(n + 1) };
// }

take(flipFlop, 5);  // => [0, 1, 0, 1, 0]