function XFindLastIndex(f, xf) {
    this.xf = xf;
    this.f = f;
    this.idx = -1;
    this.lastIdx = -1;
  }
Returns the last element of the list which matches the predicate, or
`undefined` if no element matches.

Acts as a transducer if a transformer is given in list position.

@func
@memberOf R
@since v0.1.1
@category List
@sig (a -> Boolean) -> [a] -> a | undefined
@param {Function} fn The predicate function used to determine if the element is the
desired one.
@param {Array} list The array to consider.
@return {Object} The element found, or `undefined`.
@see R.transduce
@example

     const xs = [{a: 1, b: 0}, {a:1, b: 1}];
     R.findLast(R.propEq(1, 'a'))(xs); //=> {a: 1, b: 1}
     R.findLast(R.propEq(4, 'a'))(xs); //=> undefined