Oh, Lambda Calculus. The often touted ancestor of Lisp. The underpinning of most Functional languages. Two words to bust out at a dinner party in a vain attempt to sound smart in front of your fellow programmers ¹.

At it’s most basic, Lambda Calculus states that all computations can be expressed in terms of two things: Functions and Function Application. In Ruby parlance these would be lambda { |x| x } expressions and Proc#call. That’s it ². You’ve now expressed a Turing Complete language. Numerals? Yep. Arithmetic? You bet!.

So… neat.

While one can read in many places on the web as to what the Lambda Calculus is, as well as find ample implementations of it (usually in Lisps, no less), it can often all seem a bit magical and esoteric until one encounters it in a more familiar context ³.

Basically, this has all been posturing to set you up for Tom Stuart’s excellent Programming With Nothing, which does a much finer job of breaking all of this down than I could ever hope to, all in our beloved Ruby. If you have any interest at all, do yourself a favor and read the blog post, watch the video, and (attempt to) grok the code. It really solidifies that one is capable of most any computing operation after watching Tom implement fizzbuzz ⁴ with the tiniest subset of Ruby.

Surely one could write more on the subject, and perhaps in the future I’ll even produce some original content (how shocking!), but until then, I’ve hopefully at least pointed you to some of the excellent pre-existing resources on the topic.

ps: Maruku supports footnotes! I adore footnotes. If you don’t and I’ve beaten them to death in this article, please let me know. Until then, footnotes will continue to be abused.

Ruby, oh Ruby, so deeply entrenched in mutability one can hardly trust the floor beneath them. Sure, we can have immutability by convention (ie: trust yourself and your team, clearly a foolish thought). Sure, you can kind of address this with calls to Object#freeze. Really though, at the end of the day, wouldn’t it be nice to have a native implementation of immutable data structures in our beloved Ruby? Doubly so, were they performant.

One brave developer out there, Mr. Simon Harris has set out to do just that for us.

Hamster - Efficient, Immutable, Thread-Safe Collection classes for Ruby

Hamster has been under steady development for over 2 years now and provides immutable alternatives to all of Ruby’s built in collection data structures. Hashes, Lists, Sets, Stacks, Tries, Tuples, and Vectors are all there. These are for the most part well documented in Hamster’s readme and spec suite.

Hamster achieves it’s immutability in a fashion similar to Clojure. Any operation that would in a non-functional language mutate the original object, instead will copy that object and return a new one with the updated values in place. While this is achievable with Object#dup, things can get messy quickly, and it certainly doesn’t aid in the readability of your code.

In addition to thread-safety via immutability, we also get the benefit that most operations on Hamster collections are performed lazily so their return values won’t be calculated until necessary. Languages such as Haskell have used this to great effect. In addition to intuitiveness (ie: Why calculate a value that’s unused?), lazy evaluation can sometimes lead to a much clearer expression of certain algorithms.

Is Hamster ready for the prime time? Maybe. Hamster is certainly more mature and documented than some of it’s condtenders. Do check out the readme which does a fine job pointing out potential caveats. It certainly seems worth auditioning for your next project, and since it supports an API pretty similar to native Ruby counterparts, should you have to revert one day I can’t imagine you’d encounter much pain.

If you’re interested in hearing more of what Harris has to says about immutability, you should definitely read Functional Programming in Object Oriented Languages (an excellent blog post in it’s own right).

Put yourself back in the year 2005.
Were you pushing the limits of Ruby?
Were you ruminating on Monads?

Oh yeah, me too. ;-p

But in all seriousness, way back then MenTaLguY was doing just that, and in doing so produced some of my favorite posts on Monads as they (could) apply to Ruby development.

Not only did the series help to solidify my understand of the subject, it also gave me ideas on how to use Monadic patterns in my own code.

So to kick off Functional Ruby, why don’t we deep dive into one of the more esoteric (and interesting!) topics in Functional Programming, Monads!

Part 1 introduces us to just what a monad might be. If you don’t even know what a Monad is, start here.

MenTaLguY: Monads in Ruby Part 1

Part 2 walks us through an implementation of the Identity Monad, arguably the simplest of many, and a lightweight explanation of Monadic Laws.

MenTaLguY: Monads in Ruby Part 2

Part 3 discusses Arrays as Monads (which in some circles really is the crux of a monad… sort of) and starts getting useful.

MenTaLguY: Monads in Ruby Part 3

Phew. That may have been a bit much, but why not start with a bang :)

Thanks @mentalguy!

PS: For the holdouts unconvinced of the significance of Monads, other than being a mighty fun subject in and of itself, is that it gives us a common language to talk about a pattern that emerges in our code from time to time, perhaps more often than you realize ;)

I couldn’t help but notice that the Ruby community (and the programming community at large) was buzzing with excitement over the functional programming paradigm. While there are many people and articles scattered about the net for excellent information on the subject of Ruby’s relationship with Functional Programming, I was surprised to find that no such central repository of all this wonderful content existed.

It is my hope that Functional Ruby will become that repository. I’m not sure which format would best house this content, perhaps a wiki would be better, or perhaps it would just be supplementary. However, for a first stab, let’s see how a content aggregator (with occasional original content) works out.

While I have many excellent things to share with you lined up, should you come across anything you feel shares the spirit of this site, by all means email me at rbxbxdev@gmail.com or tweet at @FunctionalRuby.

I’ve not done this before and am certainly open to feedback, so don’t hesitate to give it.

Cheers,
Robert (@rbxbx)