Rice University's Swarat Chaudhuri asks (and attempts to answer) the perennial question: why isn't functional programming more popular? I have my own long-running theory about why programming languages become popular (or don't), but first let me dispute a couple of specific things in the linked post. Chaudhuri writes:
The same survey also showed that the factor that correlates the most with preferring and using a language is the availability of libraries. This is certainly behind the meteoric rise of, say, Python. However, it seems implausible that this factor is the primary reason why functional programming is unpopular. If it were so, the F# language, which allows functional programmers to utilize the entire .NET infrastructure, would be a mainstream language by now. There’s no indication it will be any time soon.
I think Chaudhuri dismisses the hypothesis far too lightly. Here are three obvious reasons why F# is not a counterexample:
- I have never programmed in F# (although I've done a little OCaml, and I gather they're almost identical), but my long experience with cross-language interoperability makes me suspect strongly that accessing nontrivial C# libraries from F# is nothing like using libraries written idiomatically in F#. It probably feels much more like calling through a foreign function interface — for example, like accessing Java classes from Jython, except possibly worse, because C# is not only a different language but a different programming paradigm.
- There are a large variety of inevitable network effects that come from using a single language within a project. If you are going to use mostly C# libraries in the .NET ecosystem, then a sensible project manager is probably going to choose to implement the project itself in C# rather than F#. This is especially true if libraries would force you to write a lot of your code in a semi-OO style within F# anyway.
- The .NET ecosystem has never had great mindshare in the communities where most of the "hot" industrial software development is happening: open source, backend software running in the datacenter, web development, and mobile development. Spend a little time walking around Silicon Valley and San Francisco, and see how many hackers are using Windows. If, somewhere in the sea of Macbooks, you even glimpse someone using a Thinkpad, there's an excellent chance that it's running Ubuntu. Conversely, if you see someone using Windows, there's an excellent chance they're a business suit from a large corporation (at startups, even the businesspeople use Macbooks).
In fact, this was almost as true, last I checked (years ago, admittedly), even within the programming language research community. It is startling to me that a programming language researcher would look around, observe almost nobody they know hacking on Windows, and still ask why F# on .NET has not taken off.
(Mono notwithstanding, my understanding is that Microsoft has never made it a priority to make .NET development a really great experience on non-Windows platforms. C# may have a lot of libraries, but Mono has always been a second-class citizen and there is an excellent chance that large swaths of the C# ecosystem depend on APIs (or, worse, subtle implementation quirks) specific to Microsoft .NET. I suspect any prudent project manager looking at the .NET ecosystem is unlikely to bet the farm on Mono.)
Next, Chaudhuri goes on to argue that the lack of university education in functional programming is to blame. Well, I won't deny that this is a contributing factor, but: few CS schools these days teach Ruby or Perl or Objective-C, yet those languages seem reasonably popular; few CS programs teach more than rudimentary use of version control, but git (i.e. the most complex version control system known to humankind) seems popular; few CS programs teach web frontend development frameworks or MVC or template metaprogramming or MapReduce (at least, not until recently, and certainly not in intro level classes), yet all those things and many more have managed to achieve significant adoption in industry.
In short, professional developers routinely adopt all sorts of complex technologies that are not taught academically. As cool as functional programming is, I just don't believe it's fundamentally that much weirder or harder than all the things modern developers use every day. If I had told you a decade ago that in 2014, a nontrivial number of professional programmers would be writing server applications and developer tools in hand-rolled continuation-passing style, you would have looked at me funny; yet here we are!
So, then, how do I explain the relative unpopularity of functional programming languages?
First, I would observe that most programming languages are not popular, period. People have invented tens of thousands of programming languages, and nearly all of them languish in obscurity. Only a very select few manage to achieve popularity. Given that functional programming languages are a minority of all languages, we should naively expect a minority of popular languages to be functional, just from random selection. The null hypothesis does a lot of work here.
Second, I would observe that nearly all popular programming languages seem to be hybrids. Consider a different programming paradigm: Smalltalk-76 was purely "object-oriented" (everything is an object, every object has a class, every class has a superclass, objects communicate strictly by sending messages), but its most popular descendants seem to be hybrids. For example, C++, Java, and Python are not purely OO.
Therefore, we should expect that a popular functional programming language would also be a hybrid. And indeed when you view things in this light, many popular languages today have adopted bits and pieces that were once viewed as features of functional programming, such as automatic memory management, first-class lexical closures, and parametric polymorphism. Functional programming purists no doubt view this ad hoc borrowing as hopelessly inadequate cargo-cultism that misses the fundamental point of functional programming, but it is nevertheless exactly what we should expect from the gradual popularization of functional programming. In the essay Real Programming in Functional Languages (1982), J. H. Morris Jr. memorably wrote:
Functional languages as a minority doctrine in the field of programming languages bear a certain resemblance to socialism in its relation to conventional, capitalist economic doctrine. Their proponents are often brilliant intellectuals perceived to be radical and rather unrealistic by the mainstream, but little-by-little changes are made in conventional languages and economies to incorporate features of the radical proposals. Of course this never satisfies the radicals, but it represents progress of a sort.
I therefore claim that some small part of FP's "unpopularity" is apparent rather than real.
However, I admit that even the combination of the previous two explanations does not seem sufficient to explain why no primarily functional programming language has become the default way to program in a popular domain. But I don't think education is enough explanation either.
So I have to fall back on my primary theory: I maintain once again that languages reach popularity via platforms.
Thus, for example, Swift will probably be a big deal, independent of almost any qualities it has as a language. Apple is the dictator for the iOs platform. It seems likely that Apple will eventually make Swift the default way to program on iOs. Therefore, Swift will become popular, despite the fact that zero people graduating from university computer science programs in 2014 were taught Swift in school.
If functional programmers want FP to be a bigger deal, then my personal recommendation is:
- develop an industrial-quality platform for doing something that large numbers of developers really want to do, and
- evangelize the hell out of it, with a seriousness matching that of professional DevRel teams: videos, tutorials, books, portfolio-quality demo sites in GitHub, reliable turnkey commercial hosting infrastructure if need be, etc.
Web development is one good candidate domain, since (a) web development is a clusterfuck and thus ripe for improvement; (b) web developers are culturally eager to try the new hotness (in fact, arguably a little too eager); (c) you can reach a large audience without requiring any hard technology transitions of users since everyone has a web browser.
Look, for example, at how Rails lifted Ruby from relative obscurity to the default way (at least for a little while) that startups built websites in the Valley. The web framework space is more crowded today, but the field for new ones still seems fairly open, as long as you bring something new to the table. For example, focusing on realtime interaction seems to have bought Meteor a lot of buzz, despite the fact that its backend is currently built on a broken database.
Personally I think there is an opening for a "better PHP" — for all PHP's WTF/lol, if you study Keith Adams's talk "Taking PHP Seriously" (slides) it is clear that the PHP runtime does a few things right that no other platform currently does. Of course, at this point, you're probably laughing at the notion that a bunch of functional programming mandarins is going to successfully devise something for the median PHP programmer to pick up and use. But that is the type of work that might make functional programming the default way to do stuff.
EDIT: For more evidence that Chaudhuri and Hicks are wrong, see Meyerovich and Rabkin's study on language adoption.
p.s. Bizarrely, in a comment on Chaudhuri's post, Bob Harper (whom I have tremendous respect for) claims that Java doesn't have a conditional expression. What? Am I missing something?
Object x = boolExpr1 ? valExpr1 : boolExpr2 ? valExpr2 : boolExpr3 ? valExpr3 : defaultexpr;
Is this not just
cond with somewhat uglier syntax?