ramda/src/mapAccumRight.js

var _curry3 =
/*#__PURE__*/
require("./internal/_curry3");
/**
 * The `mapAccumRight` function behaves like a combination of map and reduce; it
 * applies a function to each element of a list, passing an accumulating
 * parameter from right to left, and returning a final value of this
 * accumulator together with the new list.
 *
 * Similar to [`mapAccum`](#mapAccum), except moves through the input list from
 * the right to the left.
 *
 * The iterator function receives two arguments, *acc* and *value*, and should
 * return a tuple *[acc, value]*.
 *
 * @func
 * @memberOf R
 * @since v0.10.0
 * @category List
 * @sig ((acc, x) -> (acc, y)) -> acc -> [x] -> (acc, [y])
 * @param {Function} fn The function to be called on every element of the input `list`.
 * @param {*} acc The accumulator value.
 * @param {Array} list The list to iterate over.
 * @return {*} The final, accumulated value.
 * @see R.addIndex, R.mapAccum
 * @example
 *
 *      const digits = ['1', '2', '3', '4'];
 *      const appender = (a, b) => [b + a, b + a];
 *
 *      R.mapAccumRight(appender, 5, digits); //=> ['12345', ['12345', '2345', '345', '45']]
 * @symb R.mapAccumRight(f, a, [b, c, d]) = [
 *   f(f(f(a, d)[0], c)[0], b)[0],
 *   [
 *     f(a, d)[1],
 *     f(f(a, d)[0], c)[1],
 *     f(f(f(a, d)[0], c)[0], b)[1]
 *   ]
 * ]
 */


var mapAccumRight =
/*#__PURE__*/
_curry3(function mapAccumRight(fn, acc, list) {
  var idx = list.length - 1;
  var result = [];
  var tuple = [acc];

  while (idx >= 0) {
    tuple = fn(tuple[0], list[idx]);
    result[idx] = tuple[1];
    idx -= 1;
  }

  return [tuple[0], result];
});

module.exports = mapAccumRight;