A Terser Right Fold in Java

By using Functional Java’s F2 and F3 interfaces, (functions of arity 2 and 3, respectively), I was able to make the right fold in Java look downright terse:

public static <A, B> B foldr(final F2<A, B, B> f, B z, List<A> xs) {
   return fold(curry(new F3<F<B, B>, A, B, B>() {
      public B f(final F<B, B> k, A a, B b) {
         return k.f(f.f(a, b));
      }
   }), Function.<B> id(), xs).f(z);
}
 

The curry method simply coerces an F3<A, B, C, D> by returning the equivalent F<A, F<B, F<C, D>>>.