The most elegant implementation of FizzBuzz

Sep 11, 2020 • Yehonathan Sharvit

What is FizzBuzz?

The FizzBuzz test is an interview question designed to help filter out the 99.5% of programming job candidates who can’t seem to program their way out of a wet paper bag. The text of the programming assignment is as follows:

Write a program that prints the numbers from 1 to 100. But for multiples of three print “Fizz” instead of the number and for the multiples of five print “Buzz”. For numbers which are multiples of both three and five print “FizzBuzz”

There are a lot of ways to write the FizzBuzz program. See for instance the one using Clojure pattern matching. Today, I’d like to share with you the most elegant implementation of FizzBuzz I’ve ever seen. It’s elegant because it doesn’t make use of any imperative constructs (like if statements), but only functional programming constructs (like infinite lazy sequences and function composition).

This implementation was developed by Dierk Konig and Kevlin Henney presented a Haskell version of it - in his amazing talk Declarative Thinking, Declarative Practice.

In this article, we are going to present an interactive version of Kevlin’s code in Clojure.

The elegant code

Take a look at this marvel: no if statements - only 3 infinite lazy sequences and function composition.

This is exactly what we call - Purely Functional:

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;loaded from gist: https://gist.github.com/viebel/b133efde8669d6c0630ee6895c1797c6

(defn choice [a b]

  (clojure.string/join (or (seq a) (seq b))))

​

(defn fizzbuzz [n]

  (let [fizzes (cycle ["" "" "Fizz"])

        buzzes (cycle ["" "" "" "" "Buzz"])

        words (map str fizzes buzzes)

        numbers (map str (rest (range)))]

    (take n (map max words numbers))))

the evaluation will appear here (soon)...

And it works like a charm:

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(fizzbuzz 19)

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the evaluation will appear here (soon)...

Feel free to modify 19 - the code snippets are live and interactive powered by the Klipse plugin:

1. Live: The code is executed in your browser
2. Interactive: You can modify the code and it is evaluated as you type

If you are a bit skeptic (yet) about the elegance of this implementation, you might want to read Dierk Konig’s article: he explains in details the pragmatic advantages of his code.

Further details

You probably wonder what is this choice function and why does max do when it receives 2 strings?

Well, ClojureScript runs on top of JavaScript - and in JavaScript, strings are comparable:

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(> "Fizz" "")

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the evaluation will appear here (soon)...

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(max "Fizz" "")

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But that is an ugly trick - that doesn’t work in Clojure. So it’s much better to use the choice function - that returns the first non-empty string of the two it receives:

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(choice "abc" "")

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the evaluation will appear here (soon)...

And it works also:

(fizzbuzz-clean 15)

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