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functional streams
const nats = stream(n => n + 1, 1);
const evenNumbers = map(n => n * 2, nats);
console.log(take(10, evenNumbers));
// [2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
function first(array) {
return array[0];
}
const fibs = map(first, stream(([current, next]) => [next, current + next], [0, 1]));
console.log(take(10, fibs));
// [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
function fibonacciSequence() {
function _stream(current, next) {
return {
value: current,
next() {
return _stream(next, current + next);
}
};
}
return () => _stream(0, 1);
}
const fibs = fibonacciSequence();
const firstTen = take(10, fibs);
console.log(firstTen);
// [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
const nats = stream(n => n + 1, 1);
const oddNumbers = filter(n => n % 2 !== 0, nats);
const gte42 = filter(n => n >= 42, nats);
console.log(take(10, oddNumbers));
// [1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
console.log(take(10, gte42));
// [42, 43, 44, 45, 46, 47, 48, 49, 50, 51]
function filter(fn, originalStr) {
function _stream(str) {
const { value, next } = str();
if (fn(value)) {
return {
value,
next() {
return _stream(next);
}
};
}
return _stream(next);
}
return () => _stream(originalStr);
}
function map(fn, originalStr) {
function _stream(str) {
const { value, next } = str();
return {
value: fn(value),
next() {
return _stream(next);
}
};
}
return () => _stream(originalStr);
}
function naturalNumbers() {
function _stream(n) {
return {
value: n,
next() {
return _stream(n + 1);
}
};
}
return () => _stream(1);
}
const nats = naturalNumbers();
const one = nats();
const two = one.next();
const three = two.next();
console.log(one.value);
console.log(two.value);
console.log(three.value);
function *naturalNumbers() {
let n = 1;
while (true) {
yield n++;
}
}
const nats = naturalNumbers();
console.log(nats.next().value) // 1
console.log(nats.next().value) // 2
console.log(nats.next().value) // 3
function *naturalNumbers() {
function *_naturalNumbers(n) {
yield n;
yield *_naturalNumbers(n + 1);
}
yield *_naturalNumbers(1);
}
const nats = naturalNumbers();
console.log(nats.next().value) // 1
console.log(nats.next().value) // 2
console.log(nats.next().value) // 3
const nats = naturalNumbers();
const firstTen = take(10, nats);
console.log(firstTen);
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
const nats = stream(n => n + 1, 1);
const fibs = stream(([current, next]) => [next, current + next], [0, 1]);
console.log(take(10, nats));
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
console.log(take(10, fibs));
// [0, 1, 1, 1, 1, 2, 2, 3, 3, 5, 5, 8, 8, 13, 13, 21, 21, 34, 34, 55]
function stream(fn, initial) {
function _stream(value) {
return {
value,
next() {
return _stream(fn(value));
}
};
}
return () => _stream(initial);
}
function take(n, str) {
function _take(n, str, accum) {
if (n === 0) {
return accum;
}
const { value, next } = str();
return _take(n - 1, next, accum.concat(value));
}
return _take(n, str, []);
}
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