Re: Factor

I wrote about FizzBuzz many years ago. It’s a silly programming task often cited and even included on RosettaCode. The task is described as:

Write a program that prints the integers from 1 to 100 (inclusive).

But:

• for multiples of three, print "Fizz" instead of the number;
• for multiples of five, print "Buzz" instead of the number;
• for multiples of both three and five, print "FizzBuzz" instead of the number.

This has been solved ad nauseum, but a few days ago Evan Hawn wrote about solving Fizz Buzz without conditionals or booleans using Python and the itertools.cycle function to create an infinitely iterable solution.

Let’s build this in Factor!

There are several ways to implement this, including generators, but we will be using the lists.lazy vocabulary to provide a lazy and infinite stream of values. In particular, by combining a stream of integers with a cycle of "Fizz" and a cycle of "Buzz".

The lists.circular vocabulary extends circular sequences to support the lists protocol:

IN: scratchpad USE: lists.circular

IN: scratchpad { 1 2 3 } <circular> 10 ltake list>array .
{ 1 2 3 1 2 3 1 2 3 1 }

Using that, we can create an infinite FizzBuzz list:

: lfizzbuzz ( -- list )
    1 lfrom
    { "" "" "Fizz" } <circular>
    { "" "" "" "" "Buzz" } <circular>
    lzip [ concat ] lmap-lazy lzip ;

We can print out the first few values quite simply:

IN: scratchpad lfizzbuzz 20 ltake [ first2 "%2d: %s\n" printf ] leach
 1:
 2:
 3: Fizz
 4:
 5: Buzz
 6: Fizz
 7:
 8:
 9: Fizz
10: Buzz
11:
12: Fizz
13:
14:
15: FizzBuzz
16:
17:
18: Fizz
19:
20: Buzz

And if we wanted a more traditional stream alternating between numbers and labels:

IN: scratchpad lfizzbuzz 100 ltake [ first2 [ nip ] unless-empty . ] leach
1
2
"Fizz"
4
"Buzz"
"Fizz"
7
8
"Fizz"
"Buzz"
11
"Fizz"
13
14
"FizzBuzz"
16
17
"Fizz"
19
"Buzz"
...

While not the ultimate FizzBuzz Enterprise Edition, this seems like a fun way to improve upon the simple meant for whiteboards implementation that is most often shared.