Lazy Take Model

Stop consuming a generator after enough values.
lazy-take-model A generator can describe a longer sequence while the caller decides how many values to read.
                            take
                            take = 2 (default)take = 1take = 3
                        

                            lazy_take_model.js
                        
Replay: real traced execution (multi-file project)

                            const take = 2;
const values = [];

function* squares() {
  let current = 1;
  while (current <= 5) {
    yield current * current;
    current = current + 1;
  }
}

for (const value of squares()) {
  if (values.length >= take) {
    break;
  }
  values.push(value);
}

console.log("take=" + take);
console.log("values=" + values.join(","));
const take = 1;
const values = [];

function* squares() {
  let current = 1;
  while (current <= 5) {
    yield current * current;
    current = current + 1;
  }
}

for (const value of squares()) {
  if (values.length >= take) {
    break;
  }
  values.push(value);
}

console.log("take=" + take);
console.log("values=" + values.join(","));
const take = 3;
const values = [];

function* squares() {
  let current = 1;
  while (current <= 5) {
    yield current * current;
    current = current + 1;
  }
}

for (const value of squares()) {
  if (values.length >= take) {
    break;
  }
  values.push(value);
}

console.log("take=" + take);
console.log("values=" + values.join(","));

                        
1take ← 2, values ← (empty)1const take→ 2 = 2; //@take=1, 32const values→ (empty) = [];⋯
2current ← 11const take = 2; //@take=1, 32const values = [];34function* squares() {5  let current→ 1 = 1;6  while (current <= 5) {⋯
3while (current <= 5)pass 1 of 3⋯4function* squares() {5  let current = 1;6  while (current1 <= 5) {7    yield current * current1;8    current = current + 1;⋯All 3 passes — pass 1 is the card abovepasscurrentvalues.lengthtake
11——
22——
3322
4values ← 1, current ← 1⋯5  let current = 1;6  while (current <= 5) {7    yield current→ 1 * current;8    current = current→ 2 + 1;9  }10}1112for (const value of squares()) {13  if (values.length >= take) {14    break;15  }16  values.push(value1);17}⋯values this step(empty) → 1values
5values ← 1,4, current ← 2⋯5  let current = 1;6  while (current <= 5) {7    yield current→ 2 * current;8    current = current→ 3 + 1;9  }10}1112for (const value of squares()) {13  if (values.length >= take) {14    break;15  }16  values.push(value4);17}⋯values this step1 → 1,4values
6if (values.length >= take)⋯12for (const value of squares()) {13  if (values.length2 >= take2) {14    break;15  }⋯
7console.log("take=" + take);⋯16  values.push(value);17}1819console.log("take=" + take2);20console.log("values=" + values1,4.join(","));⋯outputtake=2
values=1,4
1take ← 1, values ← (empty)1const take→ 1 = 1;2const values→ (empty) = [];⋯
2current ← 11const take = 1;2const values = [];34function* squares() {5  let current→ 1 = 1;6  while (current <= 5) {⋯
3while (current <= 5)pass 1 of 2⋯4function* squares() {5  let current = 1;6  while (current1 <= 5) {7    yield current * current1;8    current = current + 1;⋯
4values ← 1, current ← 1⋯5  let current = 1;6  while (current <= 5) {7    yield current→ 1 * current;8    current = current→ 2 + 1;9  }10}1112for (const value of squares()) {13  if (values.length >= take) {14    break;15  }16  values.push(value1);17}⋯values this step(empty) → 1values
5while (current <= 5)pass 2 of 2⋯4function* squares() {5  let current = 1;6  while (current2 <= 5) {7    yield current * current2;8    current = current + 1;⋯
6if (values.length >= take)⋯12for (const value of squares()) {13  if (values.length1 >= take1) {14    break;15  }⋯
7console.log("take=" + take);⋯16  values.push(value);17}1819console.log("take=" + take1);20console.log("values=" + values1.join(","));⋯outputtake=1
values=1
1take ← 3, values ← (empty)1const take→ 3 = 3;2const values→ (empty) = [];⋯
2current ← 11const take = 3;2const values = [];34function* squares() {5  let current→ 1 = 1;6  while (current <= 5) {⋯
3while (current <= 5)pass 1 of 4⋯4function* squares() {5  let current = 1;6  while (current1 <= 5) {7    yield current * current1;8    current = current + 1;⋯All 4 passes — pass 1 is the card abovepasscurrentvalues.lengthtake
11——
22——
33——
4433
4values ← 1, current ← 1⋯5  let current = 1;6  while (current <= 5) {7    yield current→ 1 * current;8    current = current→ 2 + 1;9  }10}1112for (const value of squares()) {13  if (values.length >= take) {14    break;15  }16  values.push(value1);17}⋯values this step(empty) → 1values
5values ← 1,4, current ← 2⋯5  let current = 1;6  while (current <= 5) {7    yield current→ 2 * current;8    current = current→ 3 + 1;9  }10}1112for (const value of squares()) {13  if (values.length >= take) {14    break;15  }16  values.push(value4);17}⋯values this step1 → 1,4values
6values ← 1,4,9, current ← 3⋯5  let current = 1;6  while (current <= 5) {7    yield current→ 3 * current;8    current = current→ 4 + 1;9  }10}1112for (const value of squares()) {13  if (values.length >= take) {14    break;15  }16  values.push(value9);17}⋯values this step1,4 → 1,4,9values
7if (values.length >= take)⋯12for (const value of squares()) {13  if (values.length3 >= take3) {14    break;15  }⋯
8console.log("take=" + take);⋯16  values.push(value);17}1819console.log("take=" + take3);20console.log("values=" + values1,4,9.join(","));⋯outputtake=3
values=1,4,9