FizzBuzz functional style inspired by @Dierk's talk on Frege

FizzBuzz.java

/**
 * FizzBuzz functional style. Inspired by @mittie's Frege talk and @kevlinhenney.
 * 
 * Uses Protonpack's {@code StreamUtils} for zipping
 * 
 * @see https://github.com/poetix/protonpack
 */
public class FizzBuzz {

	public static void main(String[] args) {

		Stream<String> numbers = IntStream.iterate(1, i -> i + 1).mapToObj(String::valueOf);
		Stream<String> fizzes = cycle("", "", "fizz");
		Stream<String> buzzes = cycle("", "", "", "", "buzz");

		Stream<String> fizzbuzz = StreamUtils.zip(fizzes, buzzes, String::concat);
		Stream<String> zipped = StreamUtils.zip(numbers, fizzbuzz, FizzBuzz::max);

		zipped.limit(100).forEach(System.out::println);
	}

	public static <T> Stream<T> cycle(T... elements) {
		return Stream.iterate(Arrays.asList(elements), i -> i).flatMap(it -> it.stream());
	}

	public static <T extends Comparable<T>> T max(T left, T right) {
		return left.compareTo(right) > 0 ? left : right;
	}
}

output.txt

1
2
fizz
4
buzz
fizz
7
8
fizz
buzz
11
fizz
13
14
fizzbuzz
16
17
fizz
19
buzz
fizz
22
23
fizz
buzz
26
fizz
28
29
fizzbuzz
31
32
fizz
34
buzz
fizz
37
38
fizz
buzz
41
fizz
43
44
fizzbuzz
46
47
fizz
49
buzz
fizz
52
53
fizz
buzz
56
fizz
58
59
fizzbuzz
61
62
fizz
64
buzz
fizz
67
68
fizz
buzz
71
fizz
73
74
fizzbuzz
76
77
fizz
79
buzz
fizz
82
83
fizz
buzz
86
fizz
88
89
fizzbuzz
91
92
fizz
94
buzz
fizz
97
98
fizz
buzz

Off by one error in the starting iterator?

That's fixed! I also extracted a few functions to make the code more readable.

Here's a Reactor version:

public class FizzBuzz {

    public static void main(String[] args) {

        Flux<String> numbers = Flux.fromStream(Stream.iterate(1, i -> i + 1))
                .map(String::valueOf);
        Flux<String> fizzes = Flux.just("", "", "fizz").repeat();
        Flux<String> buzzes = Flux.just("", "", "", "", "buzz").repeat();

        Flux<String> fizzbuzz = Flux.zip(fizzes, buzzes, String::concat);
        Flux<String> zipped = Flux.zip(numbers, fizzbuzz,
                (left, right) -> left.compareTo(right) > 0 ? left : right);

        zipped.take(100).subscribe(System.out::println);

    }
}

For the purist, the native Reactor form of numbers looks like this (there's no direct equivalent of Stream.iterate, but Flux.scan is close enough):

Flux<String> numbers = Flux.just(1).repeat().scan((i, j) -> i + 1).map(String::valueOf);

The one ; challenge :

        Flux.range(1, 100)
            .map(String::valueOf)
            .zipWith(Flux.just("", "", "fizz")
                         .repeat()
                         .zipWith(Flux.just("", "", "", "", "buzz")
                                      .repeat(), String::concat),
                    (left, right) -> left.compareTo(right) > 0 ? left : right)
            .subscribe(System.out::println);

OK @smaldini, so that gets you points for being pointless (or is it point free?). Show it to your Haskell friends.

You can cheat with FB too, as it's a repeating pattern ;-)

Function<Integer,String> n  = Object::toString;
Function<Integer,String> f  = num -> "Fizz";
Function<Integer,String> b  = num -> "Buzz";
Function<Integer,String> fb = num -> "FizzBuzz";

List<Function<Integer,String>> fns = Arrays.asList(n,n,f,n,b,f,n,n,f,b,n,f,n,n,fb);

Iterator<Function<Integer,String>> funcs = Stream.generate(() -> fns).flatMap(Collection::stream).iterator();

IntStream.range(1, 500)
         .mapToObj(i -> funcs.next().apply(i))
         .limit(205)
         .skip(200)
         .forEach(System.out::println);

Here's a Javaslang version (Gist):

import javaslang.collection.Stream;

public class FizzBuzz {

    public static void main(String[] args) {
        Stream<Integer> numbers = Stream.from(1);
        Stream<String> fizzes = Stream.of("", "", "fizz").cycle();
        Stream<String> buzzes = Stream.of("", "", "", "", "buzz").cycle();
        Stream<String> pattern = fizzes.zip(buzzes).map(t -> t._1 + t._2);
        Stream<String> fizzbuzz = numbers.zip(pattern).map(t -> t._2.isEmpty() ? String.valueOf(t._1) : t._2);

        fizzbuzz.drop(200).take(5).forEach(System.out::println);
    }

}

Output:

fizz
202
203
fizz
buzz