Blocks != Functional Programming

January 2, 2007 at 6:27 pm

Joel Spolsky is one of my heroes. He has a vast amount of insightful articles that rank among the clearest and most relevant software writing today, and his blog gets more hits in a day than mine ever will. (Speaking of which, I hit 2000 visitors yesterday – around 10x more than I ever thought I’d get.) He’s a very smart cookie, and when he speaks, people listen. But last week, while browsing the top Reddit articles of all time, I was surprised to see his article Can Your Programming Language Do This? at #4. While it’s a good primer on Javascript abstraction, I don’t think it deserves as many points as it recieved. I spent the next few days thinking about why this article bothered me so much – Joel certainly didn’t say anything untrue, attack any favorite language of mine, or make some outlandish claim. But then I realized that Joel’s article fit together in a pattern of recent articles, all of which bothered me slightly.

Here’s what I realized: it seems that every language under the sun is being evangelized as an excellent functional programming language simply because it supports a few paradigms from FP.

Or, restated: Anonymous functions do not a functional language make.

The most egregious example of a pundit claiming a language is functional when it’s clearly not is Eric Kidd’s well-known Why Ruby is an acceptable Lisp. Kidd tells us explicitly that Ruby is a denser functional language than Lisp – and I’ll be the first one to admit that if I were to debate the “denser” part of that sentence, I wouldn’t know what I was talking about.

But Ruby is not functional – Wikipedia calls it a reflective, object-oriented programming language, and I agree with them. Yes, you can have block arguments to methods, continuations, generators, reflection, and metaprogramming – but it isn’t functional, for two reasons.

1. It’s hard to carry around functions as objects.

I really don’t know why Ruby hates parentheses so much – it’s probably part of its Perl heritage. In Ruby, you can call methods without sticking superfluous parentheses in there – take a look at this Python code:



" I'll write about Cocoa soon; disaster struck the app I was writing ".strip().lower().split()



Now take a look at the equivalent Ruby code:



" Apple's releasing a tool with XCode 3 which completely supersedes my Cocoa app - so I'm very depressed right now ".strip.downcase.split



Though you could put parentheses in front of strip , downcase , and split , Ruby will work just fine without them. Now, this feature makes for far fewer parentheses, thereby making code significantly more readable. But what if I want a previously-declared function as an argument? If I type in the name, Ruby will just evaluate the function. Sure, I could use the kludge that is Symbol.to_proc, but that’s ugly – and it wraps the function inside a Proc object, which has to be called with the call(*args) method. And that’s just ugly. In Python, all you need to do is type the function’s name to use it as an object, and append a pair of parentheses if you need to call it.

2. Variables are.

A purely functional language only has immutable variables. Ruby doesn’t. (Yes, I know LISP isn’t purely functional. But it adheres to so many other FP paradigms that we can overlook that.)

But I’m getting distracted, so I’ll cut the above point short.

Anyway, what I wanted to say was this – just because your pet language has support for anonymous functions/closures doesn’t make it a functional language. Sure, Python has lambda and list comprehensions (which are taken from Haskell, a purely functional language) – but it’s not functional, it’s object-oriented. Yes, Ruby has blocks (even if you do have to wrap them in Procs), but it’s not functional. Javascript may have support for anonymous functions, but its syntax can be traced back to Algol and the birth of imperative programming language. Hell, even Objective-C has blocks if you include the F-Script framework, and it’s the farthest thing from functional there is.

In conclusion, don’t say your language is a functional one just because you borrowed a few ideas from Lisp. If you want a real functional language, try OCaml, Haskell, ML, or Scheme. Calling imperative/OOP languages functional just makes the term meaningless.

Share this: Twitter

Facebook

Like this: Like Loading... Related

Entry filed under: code, fp, oop, python, rant, ruby.