sequence.js•1.28 kB
var _curry2 = require('./internal/_curry2');
var ap = require('./ap');
var map = require('./map');
var prepend = require('./prepend');
var reduceRight = require('./reduceRight');
/**
* Transforms a [Traversable](https://github.com/fantasyland/fantasy-land#traversable)
* of [Applicative](https://github.com/fantasyland/fantasy-land#applicative) into an
* Applicative of Traversable.
*
* Dispatches to the `sequence` method of the second argument, if present.
*
* @func
* @memberOf R
* @since v0.19.0
* @category List
* @sig (Applicative f, Traversable t) => (a -> f a) -> t (f a) -> f (t a)
* @param {Function} of
* @param {*} traversable
* @return {*}
* @see R.traverse
* @example
*
* R.sequence(Maybe.of, [Just(1), Just(2), Just(3)]); //=> Just([1, 2, 3])
* R.sequence(Maybe.of, [Just(1), Just(2), Nothing()]); //=> Nothing()
*
* R.sequence(R.of, Just([1, 2, 3])); //=> [Just(1), Just(2), Just(3)]
* R.sequence(R.of, Nothing()); //=> [Nothing()]
*/
module.exports = _curry2(function sequence(of, traversable) {
return typeof traversable.sequence === 'function' ?
traversable.sequence(of) :
reduceRight(function(acc, x) { return ap(map(prepend, x), acc); },
of([]),
traversable);
});