yield.js

yield.js - a library providing functional helpers for generators

Please note that this module currently requires node.js v0.11.2 (or higher) started with --use-strict and --harmony as it makes heavy use of generators, sets and block-scoped variables.

examples

// Generator containing the sequence of natural numbers.
function* nat() {
  let i = 1;
  while (true) {
    yield i++;
  }
}

// Sequence of all Mersenne numbers.
function mersenneNumbers() {
  return y.map(nat(), function (x) { return Math.pow(2, x) - 1 });
}

// Sequence of all Mersenne numbers that are prime.
function mersennePrimes() {
  function isPrime(n) {
    return y.every(y.range(2, n - 1), function (x) { return n % x });
  }

  return y.filter(y.drop(mersenneNumbers(), 1), isPrime);
}

y.toArray(y.take(mersennePrimes(), 3)); // [3, 7, 31];

methods

fromArray(arr)

Utility function that creates a generator from a given array arr.

let g = y.fromArray([1, 2]);
yole.log(g.next().value, g.next().value); // prints 1 2

toArray(it)

Utility function that yumes the whole sequence it and returns an array containing all of its values.

function* g() {
  yield 1;
  yield 2;
  yield 3;
}

y.toArray(g()); // [1, 2, 3]

range(from, to)

Creates a generator containing an arithmetic progression starting with the value from up to including value to.

y.toArray(y.range(1, 3)); // [1, 2, 3]

map(it, fun)

Creates a generator containing the results of applying fun to all values of it.

function square(x) {
  return x * x;
}

y.toArray(y.map(y.range(1, 3), square)); // [1, 4, 9]
y.toArray(y.map([-1, -2, -3], square)); // [1, 4, 9]

filter(it, p)

Creates a generator containing values of it where the predicate p holds.

function odd(x) {
  return x % 2;
}

y.toArray(y.filter(y.range(1, 6), odd)); // [1, 3, 5]
y.toArray(y.filter([1, 2, 3, 4], odd)); // [1, 3]

reject(it, p)

Creates a generator containing values of it where the predicate p does not hold.

function odd(x) {
  return x % 2;
}

y.toArray(y.reject(y.range(1, 6), odd)); // [2, 4, 6]
y.toArray(y.reject([1, 2, 3, 4], odd)); // [2, 4]

compact(it)

Creates a generator containing all truthy values of it.

y.toArray(y.compact(y.range(-1, 1))); // [-1, 1]
y.toArray(y.compact([1, "", 2, 0, true, false])); // [1, 2, true]

reduce(it, fun)

Consumes the whole sequence it and reduces all of its values down to a single value. fun is called on each step with the current reduction state and value as arguments.

function sum(it) {
  return y.reduce(it, function (acc, x) { return acc + x }, 0);
}

sum([2, 3, 4]); // 9
sum(y.range(1, 3)); // 6
sum(y.range(-1, 1)); // 0

each(it, fun)

Consumes the whole sequence it calling the given function fun for every value, passing the value as a single argument.

// Show alert boxes for numbers 1 to 3.
y.each(y.range(1, 3), alert);
y.each([1, 2, 3], alert);

min(it)

Consumes the whole sequence it and returns the minimum value found or +Infinity for empty sequences.

y.min(y.range(1, 6)); // 1
y.min([5, 1, 7]); // 1

max(it)

Consumes the whole sequence it and returns the maximum value found or -Infinity for empty sequences.

y.max(y.range(1, 6)); // 6
y.max([5, 1, 7]); // 7

uniq(it)

Returns a generator containing all distinct values from the given sequence it.

function mod3(x) {
  return x % 3;
}

y.uniq(y.map(y.range(1, 9), mod3)); // [1, 2, 0]
y.uniq(['a', 'b', 'a', 'c']); // ['a', 'b', 'c']

every(it, p)

Returns true if the given predicate p holds for all values of the given sequence it. Returns true as well for empty sequences.

function greaterThanZero(x) {
  return x > 0;
}

y.every(y.range(1, 5), greaterThanZero); // true
y.every([0, 1, 2, 3, 4], greaterThanZero); // false
y.every([], greaterThanZero), true);

some(it, p)

Returns true if the given predicate p holds for at least one value of the given sequence it. Returns false for empty sequences.

function equalToZero(x) {
  return x === 0;
}

y.some(y.range(1, 5), equalToZero); // false
y.some([0, 1, 2, 3, 4], equalToZero); // true
y.some([], equalToZero), false);

size(it)

Consumes the whole sequence it and returns the number of values found.

y.size(y.range(1, 5)); // 5
y.size([1, 2, 3]); // 3

contains(it, val)

Returns true if the given value val is contained in the given sequence it, false otherwise.

y.contains(y.range(0, 5), 0); // true
y.contains([1, 2, 3, 4, 5], 0); // false

find(it, p)

Returns the first value of the given sequence it for which the given predicate p holds.

function greaterThanThree(x) {
  return x > 3;
}

y.find(y.range(1, 6), greaterThanThree); // 4
y.find([3, 4, 5], greaterThanThree); // 4
y.find([], greaterThanThree); // undefined

take(it, num)

Returns a generator containing the first num values from the given sequence it.

y.take(y.range(1, 6), 3); // [1, 2, 3]
y.take([1, 2, 3], 2); // [1, 2]

drop(it, num)

Returns a generator containing all but the first num values from the given sequence it.

y.drop(y.range(1, 6), 3); // [4, 5, 6]
y.drop([1, 2, 3], 1); // [2, 3]

flatten(it)

Flattens the given (nested) sequence it.

function* g() {
  yield 1;
  yield 2;
  yield [3, 4];
}

y.flatten([0, g()]); // [0, 1, 2, 3, 4]
y.flatten([1, [2], [3, [[4]]]]); // [1, 2, 3, 4]

flattenOnce(it)

Flattens the given (nested) sequence it by a single level.

y.flattenOnce([1, [2], [3, [[4]]]]); // [1, 2, 3, [[4]]]

flatMap(it, fun)

Creates a generator by applying fun to all values of it and using the elements of the resulting sequences.

function map(x) {
  return [x, x];
}

y.flatMap(y.range(1, 3), map); // [1, 1, 2, 2, 3, 3]
y.flatMap([1, 2, 3], map); // [1, 1, 2, 2, 3, 3]
y.flatMap([1, [2]], map); // [1, 1, [2], [2]]

union(it [, it2, ...])

Creates a generator containing the union of all passed sequences.

y.union(y.range(1, 3), [2, 3, 4], y.range(1, 6)); // [1, 2, 3, 4, 5, 6]

difference(it, oth [, oth2, ...])

Creates a generator containing all values of it that are not contained in oth and all further given sequences.

y.difference(y.range(1, 6), [3, 4], y.range(1, 2)); // [5, 6]

without(it, val [, val2, ...])

Creates a generator containing all values of it that do not match val or any other of the given values.

y.without(y.range(1, 6), 1, 2); // [3, 4, 5, 6]
y.without([1, 2, 3, 4], 1, 2); // [3, 4]

partition(it, p)

Partitions the given sequence it according to the given predicate p. It returns an array with the first entry containing a generator with all values of it for which the predicate p holds. The second entry will contain a generator with all values for which the predicate does not hold.

function greaterThanThree(x) {
  return x > 3;
}

y.partition(y.range(1, 6), greaterThanThree); // [[4, 5, 6], [1, 2, 3]]
y.partition([2, 3, 4, 5], greaterThanThree); // [[4, 5], [2, 3]]

install

For node.js, with npm do:

npm install yield

todos

• Use yield* when implemented.
• Use for...of when implemented.
• Use rest parameters when implemented.

license

MIT