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FizzBuzz in Smalltalk

Donald Raab

5 min read·<br>1 day ago

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Accept the things you can’t change. Change the things you can’t accept.

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Wait, wut?

The Smalltalk Magic Trick<br>Amidst all of the discussion over basic language syntax and library depth, developers who only program in languages like Java miss the true power of a language like Smalltalk.<br>Smalltalk is evolvable.

You can change the system.<br>The Inline FizzBuzz Approach<br>I decided to sit down and solve the FizzBuzz problem in Smalltalk. I had posted a blog with my Java based solution on StackOverflow from a decade ago.<br>Ternary, Predicate, and Pattern Matching for FizzBuzz with Java 26<br>Ternary, Predicate, and Pattern Matching for FizzBuzz with Java 26. Exploring FizzBuzz solutions from Java 8 to Java…

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I started with the “simplest” possible solution which only requires inlining code as follows.<br>Press enter or click to view image in full size

FizzBuzz in Smalltalk using inlined codeHere’s the source for the inline approach:<br>(0 to: 20) collect: [ :each |<br>(each isDivisibleBy: 3)<br>ifTrue: [<br>(each isDivisibleBy: 5)<br>ifTrue: [ 'FizzBuzz' ]<br>ifFalse: [ 'Fizz' ]<br>ifFalse: [<br>(each isDivisibleBy: 5)<br>ifTrue: [ 'Buzz' ]<br>ifFalse: [ seach ]<br>]The code (0 to: 20) creates an Interval. Then I send the collect: message, which takes a one argument BlockClosure, to the Interval. Then we see a bunch of Boolean messages with blocks (i.e. ifTrue:ifFalse:). If you read my recent blog on Smalltalk Blocks, you’ll learn that Smalltalk doesn’t have an if-statement. Control structures are achieved in Smalltalk using messages and blocks.<br>Smalltalk Blocks<br>Smalltalk Blocks. The expression of the square bracket.

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The message isDivisibleBy: is available on Number types in Smalltalk. It is a more human readable form of i % n == 0 in Java, which I read in my brain as “i mod n equals zero.”<br>We can see the definition of isDivisibleBy: on the Number class in Smalltalk.

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The method isDivisibleBy: on Number in Smalltalk

This implementation should explain why I used isDivisibleBy: instead of (i \\ n) = 0. Any developer can read isDivisibleBy: but I would have to explain that \\ is mod in Smalltalk, instead of % like in Java. That would lose folks quickly, but now you know.<br>Evolving the Integer Class to Include fizzBuzz<br>Now I’m hoping since you see a method named isDivisibleBy: on Number, you may have had a lightbulb go off in your head.<br>Can we add other methods to numbers? 💡

Yes. Yes we can.<br>Let’s add a fizzBuzz method to the Integer class.

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Adding fizzBuzz to the Integer class in Smalltalk

Now, I just went to the Integer class and added a method by typing in an empty method template. Easy! When I used to pogram in Smalltalk, we would use a slightly different approach for extending existing classes via extension methods that we wanted to share in multiple projects. I will leave that to the reader to discover that capability in Pharo Smalltalk. For my purposes here, it is enough to show that we can change existing library classes.<br>Here’s the source for the fizzBuzz method.<br>fizzBuzz<br>^(self isDivisibleBy: 3)<br>ifTrue: [<br>(self isDivisibleBy: 5)<br>ifTrue: [ 'FizzBuzz' ]<br>ifFalse: [ 'Fizz' ]<br>ifFalse: [<br>(self isDivisibleBy: 5)<br>ifTrue: [ 'Buzz' ]<br>ifFalse: [ self ]<br>]This code looks almost identical to the code I used inline. The name fizzBuzz at the top is the method signature. The ^ is the return character in Smalltalk. The reserved word self in this context refers to the instance of the Integer class.<br>Here’s a test for the fizzBuzz method.

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FizzBuzzTest

Now that we have a fizzBuzz method on Integer we can write the code as follows, and never have to write fizzBuzz algorithm by hand again.

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Using fizzBuzz on the Integer class with an Interval

The source is as follows:<br>|fizzBuzz|

fizzBuzz := (0 to: 20) collect: [:each | each fizzBuzz]The |fizzBuz| sets up a local variable. The := assigns the result of code on the right to the variable on the left. I used a one argument BlockClosure with collect: here. I can simplify this to use a Symbol as follows:<br>|fizzBuzz|

fizzBuzz := (0 to: 20) collect: #fizzBuzzA Symbol in Smalltalk is a unique String that can be used as a key, or as a replacement for a Block as I’ve used it here. Why does this work? Let’s look at the value: method on Symbol which is the equivalent method that would be called on BlockClosure.

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The value: method as defined on the Symbol class which allows a Symbol to behave like a BlockClosure.

That’s All Folks!<br>I thought it would be fun to round out a final Smalltalk blog for June 2026 with...