/**
 * Reduce `arr` with `fn`.
 *
 * @param {Array} arr
 * @param {Function} fn
 * @param {Mixed} initial
 *
 * TODO: combatible error handling?
 */

module.exports = function(arr, fn, initial){  
  var idx = 0;
  var len = arr.length;
  var curr = arguments.length == 3
    ? initial
    : arr[idx++];

  while (idx < len) {
    curr = fn.call(null, curr, arr[idx], ++idx, arr);
  }
  
  return curr;
};