If you read Planet Perl Iron Man (and you should) or listen to the discussions of the corehackers project, you may have seen more discussion about Perl 5's DarkPAN problem.

One of the big tensions in the Perl 5 world is between progress and stability. (I use both terms with the same sense of distaste I hear the terms "pro-choice" and "pro-life". Then again, I sympathize with linguistic prescriptivism, if only to clarify motives and intent.)

"Perl 5 must change," some people cry. "There's no good reason Perl shouldn't enable strictures and warnings by default for all new programs!"

"Perl 5 cannot change," retort others. "There's too much existing code to change Perl's behavior!"

I find the latter argument ridiculous such that withering mockery is the only good response. That's rarely useful, however.

When people say "Perl 5 cannot change its default behavior!", I believe they have in mind several other points. Some of them are good points. Yet until the Perl community as a whole can address those points directly, we'll remain at an impasse. (The word "impasse" overstates things; to a man, the active Perl 5 pumpkings appear to hew strongly to the "Change is painful and bad and wrong" philosophy, even going as far to say that frequent releases are undesirable hassles because stat calls are not cheap.)

Translation to English of Various Meanings of "Stability Über Alles"

With that in mind, here are several possible meanings of "You can't change default behavior!

Distributors may upgrade Perl 5 in their installations and may have to upgrade packages which depend on Perl 5 to work with the new version. This is true. This is what distributors do. This is what distributors do with all of their dependencies. This is why distributors exist. This is also only a problem if no optional mechanism of disabling new features exists -- and such a feature needs to exist.

Changing Perl 5's default behavior may render existing tutorials and examples obsolete. Good. Many existing examples of Perl 5 code are horrible. A steadfast refusal to run unmaintainable code may even encourage the creation of better tutorials and the publication of better examples.

Existing code -- left untouched for a decade -- may suddenly break. I don't understand this point. I ran into Perl 4 code the other day. Somehow the last sixteen years of Perl 5 releases have not yet managed to erase all perl4 binaries -- as well as the Perl 4 source code -- from the world's hard drives and tape drives and USB drives. Why should anyone believe that Perl 5.10.0 will not be available when Perl 5.10.1 comes out? Ditto Perl 5.12.0. Sometimes this argument has nuance to it. We must use a version of Perl supported by a vendor to whom we offer supplications of fresh fruits, wines, native crafts, and large checks. In other words, you're paying for the privilege of not upgrading. Good for you. Go bug the organization you're paying. That's why you're paying them. Sometimes this argument indicates that the arguer has no business working with computers in a professional setting. We don't know what software we're running and we won't know what will break if we upgrade and we don't know how to fix it if it does. If that's you, write your stakeholders a letter suggesting that they try to avoid upgrading, ever. Then find another line of work, perhaps something involving no technology more complex than one rock stacked atop another. If you can't test your software against newer dependencies, identify any potential problems, and work with upstream to resolve those issues before you perform an upgrade -- or if you're unwilling to do so -- then you are dangerously incompetent. That kind of incompetence is not the Perl community's responsibility. Don't short your stock, either -- that smacks of insider trading.

Frequent, experimental, zig-zag changes to Perl 5 syntax and semantics will be confusing! Yeah. That's why no one's suggested doing them. Suggesting that Perl 5 could use real function signatures or strictures-on-by-default is very different from throwing every potential combination of hash-and-array-sort function into one big global namespace. The desire to add missing features and the desire for more frequent releases by no means implies a lack of foresight or holistic design, nor a lack of comprehensive testing, nor thoughtful refinement of an idea and implementation to the point where it's obviously right.

Changes mean bugs, and we can't have bugs! There are already bugs. There are already regressions -- including a performance regression that would have affected only a few people if a stable 5.10.1 had come out in early 2008. The only way to avoid bugs altogether is to avoid writing software. The best you can do is make them unlikely, catch them early, and fix them quickly (remembering that unreleased software may as well not exist to your users).

It's irresponsible to break someone else's code, especially if you can't see it. It's insane to support invisible code that may not even exist.

There are so many competing implementations of this idea on the CPAN, it's obvious there's no one right way to do things! There are so many competing implementations of this idea on the CPAN because there's no obvious good, default, built-in way to do things.

My code has to run on several different major versions of Perl; I can't take advantage of these new features. You have a change management problem. Not me.

I can't show you a test case, but this change breaks my code! There's an invisible sign on the road by my house that gives me the right to charge a $5 toll. Pay up.

This is the way it's always been. How's that working out?

A More Serious Take on Stability

Change doesn't have to be painful. Change doesn't have to be chaotic. It's possible to meet many of the real underlying goals with technical means.

The problem isn't technical, however. It's social. It's fear.

This is the fear of risk -- the risk that unknown problems lurk in seemingly minor changes. This is also the fear of the risk that the cost of mitigating this risk is too high. This is especially the fear of the risk that changing Perl 5 will appear so expensive that people will stop using it.

With all of that mockery out of the way, perhaps the Perl community can have a sober assesment of risk, bereft of fears and stupid technical blatherings that serve only to obscure the real question:

Whose needs do the features and policies and strategies and goals and visions of Perl 5 development serve?

Change for the sake of change itself is useless. Stability for the sake of stability is equally useless. No one wants complete stability or complete chaos. (Even if you think you want complete stability, you don't; when you find a bug or a typo or a confusing section of documentation, you've found a place where perfect stability gets in your way.)

(You'd almost think the Perl 5 community didn't have a few experienced project managers, methodologists, risk managers, and software developers, if not several thousand people who know how to create, maintain, sustain, and release free software projects.)

There must be a middle ground. There must be a way to identify real needs, prioritize useful changes, and deliver those changes to stakeholders in an efficient and effective fashion. I reject the false dilemmas which state that we have to make a choice between relentless, plodding conservatism and Psychotic Hyperactive Purposless-esque change...

... especially when the alternative is to suggest that every file containing modern Perl code start with a wall of boilerplate:

use 5.010; use strict; use warnings; use utf8; use Carp; use Want; use CLASS; use SUPER; use autodie; use autobox; use signatures; use mro 'c3'; use IO::Handle; use File::stat; use autobox::Core; use UNIVERSAL::ref;

I hate to channel John Stuart Mill, but if Perl 5 stays like that for long, it won't be a language suitable for novices to write new programs. It'll be merely a great language to maintain code written in the late '90s not yet replaced with something with slightly saner defaults.

That would be a pity.