unfold.js•1.21 kB
var _curry2 = require('./internal/_curry2');
/**
* Builds a list from a seed value. Accepts an iterator function, which returns
* either false to stop iteration or an array of length 2 containing the value
* to add to the resulting list and the seed to be used in the next call to the
* iterator function.
*
* The iterator function receives one argument: *(seed)*.
*
* @func
* @memberOf R
* @since v0.10.0
* @category List
* @sig (a -> [b]) -> * -> [b]
* @param {Function} fn The iterator function. receives one argument, `seed`, and returns
* either false to quit iteration or an array of length two to proceed. The element
* at index 0 of this array will be added to the resulting array, and the element
* at index 1 will be passed to the next call to `fn`.
* @param {*} seed The seed value.
* @return {Array} The final list.
* @example
*
* var f = n => n > 50 ? false : [-n, n + 10];
* R.unfold(f, 10); //=> [-10, -20, -30, -40, -50]
*/
module.exports = _curry2(function unfold(fn, seed) {
var pair = fn(seed);
var result = [];
while (pair && pair.length) {
result[result.length] = pair[0];
pair = fn(pair[1]);
}
return result;
});