Chunky Bacon in the Land of Lisp: a Rubyist Becomes Intimately Acquainted with Parentheses

Ruby is Awesome

Like many Rubyists, I came to the language through Rails while fleeing the horror of convoluted PHP sphagetti hell. For web development, the Rails framework was a relief; for programming, Ruby was a revelation.

When asked, most other Ruby programmers I know will say they feel the same way. Ruby was designed to make programmers happy and it shows. Ruby is remarkably free of cruft. Its succinctness and cohesion allow you to go from idea to implementation quickly.

What this all boils down to is that Ruby requires far less "mental overhead", leaving room for creative problem solving. Our memories and attention spans are limited, and every time we get caught up in the weird minutiae of a programming language we're likely to forget what we were trying to do in the first place. We then need to piece together our original purpose and plan of attack, breaking our flow and causing frustration. Because Ruby introduces less of a cognitive burden, we're able to stay "in the zone" longer and experience the pleasure of creativity.

In addition to its design, Ruby offers power and flexibility. As in the old Perl mantra, it makes easy things easy and hard things possible through such features as closures, meta programming, mixins, message passing and "duck typing". All of these ideas were new to me back in 2005 when I got my first taste of Ruby, and it was so exciting to learn about them and use them that for months I spent almost every morning and evening seeing what I could do with this awesome language.

Lisp is Awesome

It's been awhile since I've felt this excited about a language. Javascript, which I pretty much learned in tandem with Ruby, was a lot of fun. Objective-C was frustrating because I didn't know C and couldn't find a comprehensive guide to the mammoth framework(s?) used for cocoa development. Learning C was a fun challenge and it's been useful in understanding Unix, but it hasn't really sustained my interest.

And now I've met Lisp. Common Lisp, to be exact. And I find myself just as excited as when I started learning Ruby. I don't even really know what I would use the language for - it's just fun to learn it and see what I can do. For the time being, I've been occupying myself with implementing Tic-Tac-Toe in Lisp and Ruby, as I wrote about in my article on minimax. (By the way - I plan on writing an article comparing the two versions.) Next I plan to optimize those implementations a little bit, and after that I shall work on my magnum opus: Hobbit vs. Giant.

But back to Lisp. Like with Ruby, the language does not get in my way. And just like when I came from PHP, I'm finding myself with a wealth of new ideas and programming tools to play with. Generic functions and classes, multi-methods, first-class treatment of functions and closures - the list could go on. But chief among Lisp's features is the mighty macro.

Macros are Awesome

One thing that really blew my mind about Ruby is the power you get from its meta-programming. Though I've barely scratched the surface in Lisp, I have the sense that Lisp's macro system offers so much more.

It's hard for me to explain why I think macros are cool except by analogy. So - consider that, in Ruby, everything is an object. This simplifying concept reduces cognitive burden, but it also means that you can extend Ruby's power to everything. You can open up the String class and define methods on it because it's just a class like every other.

In Lisp, code is data. What this means is that the code you write to do stuff takes the same form as the code you write to represent a basic Lisp data structure, the list. For example, this is how you would add two numbers in Lisp:

( + 1 2 )

Now consider how you would write a list constant:

'(+ 1 2)

The single quote indicates, "Don't evaluate me, just use me as data".

Because the code that you write in order to do stuff takes the same form as a list, Lisp is able to treat code as data and use the full power of the language to manipulate your code.

This is what gives macros their power. By contrast, in Ruby you perform metaprogramming largely through string manipulation and symbols, As Peter Seibel explains in Practical Common Lisp:

The key to understanding macros is to be quite clear about the distinction between the code that generates code ( macros ) and the code that eventually makes up the program ( everything else ) . When you write macros , you 're writing programs that will be used by the compiler to generate the code that will then be compiled . Only after all the macros have been fully expanded and the resulting code compiled can the program actually be run . The time when macros run is called macro expansion time ; this is distinct from runtime , when regular code , including the code generated by macros , runs .

As I write this, I find that I'm not really doing the subject justice. That's probably inevitable. Before really learning what closures are and how to use them, most Rubyists probably didn't see what the big deal was. However, I hope that this explanation might inspire other Rubyists did give this language a try. My guess is that most who really give it a shot will come to enjoy it as I do. The point is that Lisp offers a great deal of power and flexibility in an elegant package, all language aspects that Rubyists appreciate. The territory is worth exploring.

Lisp Resources

To get started, I recommend Land of Lisp: Learn to Program in Lisp, One Game at a Time!. I would say that it rivals _why's book in fun, creativity, and usefulness.

As a follow-up, I recommend the aforementioned Practical Common Lisp. It's also a good choice to get started immediately as it's available online for free. (Incidentally, it's quite pleasant to read as the typography is good.) It's similar to the Pickaxe in that it gives a much more thorough and straightforward explanation of the language. It has really helped me fill in the gaps. The following resources are also useful:

r/lisp - It's fun to see what's going on in the lisp world. The community has also been friendly and helpful.

The Common Lisp HyperSpec - The master CL reference.

On Lisp - Paul Graham's classic, for free. I haven't actually started this one yet but I'll be going through it next.

Let Over Lambda - I've only just started this and it's probably too advanced for me, but holy crap is it exciting to read!

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