Flying Machine Studios
adventures in making stuff with Daniel Higginbotham

Why Clojure's a Great Next Language for Rubyists

11 November 2015

HAVE frothing at the mouth YOU flailing arms CONSIDERED eyes are unfocused and mad LISP flipping furniture over

— @ra

If you're a Rubyist itching to learn a new language, then I want to convince you (using only a minimum of mouth frothing and chair flipping) that Clojure's a great pick for you. Please excuse me if this article reeks of the glassy-eyed fanaticism of the true believer, but the fact is that I think Clojure is crazy stupid fun to use, and intellectually rewarding to boot.

I fell in love with Ruby back in 2005, and since then only Clojure has been able to elicit the same level of affection. I think this is because Clojure has the same fundamental attributes that make Ruby so appealing: it's simple, it's powerful, and above all, it's fun. The rest of this love letter cough I mean, blog article, is about how Ruby and Clojure exhibit these attributes in very different ways, and how Clojure's different approach to computation makes it fascinating and rewarding to learn.

My first exposure to Ruby was DHH's whoops-laden Ruby on Rails demo. That video saved me from the Lovecraftian horror that was PHP circa 2005. You may have had a similar experience, with Ruby rescuing you from C++ or Java or COBOL or whatever.

It's a vast understatement to say that, compared to PHP, Ruby is elegant. Whereas PHP seemed almost to strive for inconsistency, Ruby employs only a few, simple ideas: everything is an object, you advance your program by sending messagse to objects, and message dispatch is governed by a couple easily-understood rules.

Clojure is also a very simple language. It wouldn't be a stretch to say that simplicity is one of the core tenets of the Clojure philosophy; its creator, Rich Hickey, has given a number of talks elaborating on what it means for something to be simple, including Simple Made Easy and Clojure, Made Simple.

Clojure's simplicity, however, takes a radically different form. In Clojure, you primarily care about two things: data and functions. You pass data to functions and get new data back. Yes, there's other interesting stuff like state management constructs and macros, just as there are other interesting aspects of Ruby like modules and blocks. But the heart of Clojure is so simple any eighth grade algebra student can understand it: hand some value to a function, and it hands you a new value back.

"But wait a minute," you might be thinking, "You can't just pass data around like that. Haven't you read POODR? What about encapsulation? What if those functions mutate your data?"

In Clojure, data is immutable. You can't change existing data, you can only derive new data; when you add 3 and 4, you don't change 3 or 4 to make 7, you derive 7. If this sounds crazypants and impossible to work with, all I can do is assure you that it does work (and point you to this book I wrote available free online, Clojure for the Brave and True which explains how) and hope that your intellectual curiosity will motivate you to explore this crazypants paradigm that lots of people seem to love. Here's a teaser: many of the problems addressed by object-oriented design simply aren't problems in Clojure. You don't have to care about inheritance vs. composition because behavior isn't chained to data. You don't have to care about data hiding because there's no risk that some object somewhere will silently change it.

As a Rubyist, you know that simplicity buys you power, where power is defined as the ability to express computational ideas concisely. For example, Ruby's blocks allow you to write anonymous algorithms, something that's impossible in C. Another example: Ruby's simple method dispatch scheme makes it easy for you to reason about and design robust programs. It lets you easily extend code and buys you reuse through multiple inheritance. Most enticingly, it lets you do metaprogramming.

Clojure's simplicity also buys you power. As a Lisp, Clojure employs a syntax which just so happens to mirror the internal abstract syntax trees that represent Clojure code. I'm going to wave my hands a bit here and say that this lets you use macros, the most powerful metaprogramming tool available to any language. In the Ruby community, we like to talk about code that writes code; macros take this idea to a whole different level. It's not an exaggeration to say that Ruby's metaprogramming system provides only a subset of the capability provided by Lisp macros.

Super duper hand wavy, I know, but the point is: if you like how powerful Ruby is, you will lose your flipping mind over how powerful Clojure is. Macros let you easily implement ideas from all corners of computer science. It's not an accident that Clojure has so many libraries that let you use different paradigms. There's core.logic for logic programming, instaparse for building parser generators, core.typed for haskell-ish typed programming, and much more.

And macros aren't even the coolest part. I'll let you in on a secret: macros are the flashy, shiny bait that wild-eyed Clojurists lay out to ensnare curious programmers. Nay, even more powerful is Clojure's design of programming to abstractions. This design makes it incredibly easy to reuse your code and extend existing code. Of course I can't tell you how in the short space afforded by this digital outburst, but you'll grow as a programmer if you learn about it.

These last two paragraphs also hint at what makes Clojure so dadgum fun. First, by learning Clojure you get introduced to one of the most loved and respected computational traditions, Lisp and the lambda calculus. It also has a clear philosophy, articulated by Rich Hickey, that will make you a better programmer. Not only that, other programming vistas become more readily accessible.

Second, Clojure is a joy to write. Here's a quote from Matz (Ruby's creator) on his design philosophy:

By using Ruby, I want to concentrate the things I do, not the magical rules of the language, like starting with public void something something something to say, "print hello world." I just want to say, "print this!" I don't want all the surrounding magic keywords. I just want to concentrate on the task. That's the basic idea. So I have tried to make Ruby code concise and succinct.

Clojure, likewise, is concise. It lets you focus on solving the problem at hand rather than figuring out the magic whatever. People are falling in love with Clojure, spending their nights and weekends learning it hacking with it, because the experience is its own reward.

If you're looking to stretch yourself and explore more of what the world of programming has to offer, then I recommend Clojure to you with all of my crazed heart. Here are some resources for getting started:

Now go out there and start learning some Clojure!

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