Polyglot programming (the practice of knowing and using many programming languages) seems to be all the rage these days. Its adherents claim two benefits:
- Using the right tool for every job means everything you do is a little bit easier (or better, or faster, or all of the above).
- Knowing multiple programming paradigm expands your mind and makes you better at programming in every language.
What I don't like is the conclusion that this means you should always use the right tool for the job. What, you the astute reader asks, does this mean you think we should use the wrong tool for the job? No, that would be idiotic, it means I think sometimes using the less optimal tool for the job carries overall benefits.
So what are the dangers of being a polyglot programmers (or the benefits of not being one, if you will)?
Using multiple languages (or any technology) stresses your operations people. It's another piece they have to maintain. If you've got a nice JVM stack, top to bottom, with nice logging and monitoring do you think your ops people really want to hear that they need to duplicate that setup so you can run three Ruby cron jobs? No, they're going to tell you to suck it up and write it up and either see if JRuby works or use Clojure or something, because 1% of your company's code isn't worth doubling their work.
Another risk is that it raises the requirements for all the other developers on the project. Martin Golding said, "Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live." Imagine when you leave your job and the next guy finds out you decided to write some data analysis scripts in APL (for those of you who don't remember, APL is that lovely language that doesn't use ASCII characters). It's fine to use APL if that's something you can require of new hires, it's not fine when your job says "Python developer" (it may actually work for Perl developers, but I assure you it'll be purely coincidental). Learning a new language is hard, learning to write it effectively is harder. Learning a new language for every script you have to maintain is downright painful, and once you know all of them, context switching isn't free for either humans or computers.
I'm not saying write everything in one language, that'd probably leave you writing a lot of code in very suboptimal languages. But choose two or three, not ten. Your ops people will thank you, and so will the guys who have to maintain your code in a decade. At DjangoCon this year Glyph Lefkowitz actually went farther, he argued that not just the code you write, but your entire technology stack should be in one language. But that's a separate discussion, you should watch the video though.
Also, because I'm a big fan of The West Wing, I'd be remiss if I used the word polyglot this many times without linking to a great scene.