lib/foldl.js

'use strict';

Object.defineProperty(exports, "__esModule", {
    value: true
});
exports.foldl = foldl;

var _head = require('./head');

/**
 * Applies a function against an accumulator and each value of the list from left-to-right
 * to reduce it to a single value. (also known variously as reduce).
 *
 * @since v0.1.0
 * @param {Function} fn - The accumlating function, the function to
 * execute on each value in the array
 * @param {Array} list - The list we should accumlate
 * @param {any} accumlator -
 * @param {number} index -
 * @return {any}
 * @example
 *   const add = (prev, current) => prev + current
 *   foldl(add)([1, 2, 3]) // => 6
 */
function foldl(fn) {
    return function (list) {
        var accumulator = arguments.length <= 1 || arguments[1] === undefined ? (0, _head.head)(list) : arguments[1];
        var index = arguments.length <= 2 || arguments[2] === undefined ? 0 : arguments[2];

        var result = void 0;
        if (index === list.length - 1) {
            result = accumulator;
        } else {
            accumulator = fn(accumulator, list[index + 1]);
            result = foldl(fn)(list, accumulator, index + 1);
        }
        return result;
    };
}