Fun at the Turing tar pit

January 24th, 2008

I love to babble about "social issues of software development". I try to avoid mentioning them in technical discussions (also known as "flame wars") because it makes a particularly lousy argument. Other than that, I just love talking about it. Face it: software is written by people for people. Most of it smells like a hairless pink ape. Nothing formal or provable/refutable or scientific or universally correct about it. People stuff. Like furniture, or jewelry, or porn, or screwdrivers. The machine merely follows orders, the humans are the serious players. Social Issues are what makes those bits move.

So, Social Issues. Today's Social Issue is this: programmers adore Turing tar pits. Turing tar pits are addictive. You can render programmers completely paralyzed from any practical standpoint by showing them a tar pit and convincing them to jump into it.

A Turing tar pit is a Turing-complete virtual machine that doesn't support straightforward implementation of bread-and-butter programmer stuff. Bread-and-butter programmer stuff includes arithmetics, variables, loops, data structures, functions and modules and other such trivial and awfully handy goodies. A canonical example of a Turing tar pit is the Brainfuck programming language. Implementing a decimal calculator or a sokoban game in sed is also a consensus example of Turing tar pit swimming as far as I know. By "consensus", I mean that nobody writes software that people are actually supposed to use on top of those VMs.

Some Turing tar pits are used as vehicles for production code.

C++ templates. A crippled everything-is-a-type VM. Try writing a compile-time loop using them; then, try to implement a compile-time hash table. I find the implementation of a decimal calculator in sed more concise in certain aspects. But people do awfully hairy things with C++ templates, like boost. The fun of implementing such things can only be compared to the fun of using them (error messages which would take a whole tree to print out on paper and such).

TeX. A crippled everything-is-a-text-transformation VM. A great back-end with a nightmarish front-end, as far as I can tell. You get neither WYSIWYG nor the ability to mechanically analyze the content (the document is basically code which transforms itself, and transforms itself, and transforms itself, and you can't make any sense of the document without, um, running it). But people do unimaginably hairy things on top of TeX, like LaTeX. You actually have to debug LaTeX documents, and I bet that the best TeX debugger is somewhat worse than the worst C debugger out there.

Shell scripts. A crippled everything-is-a-process-unless-it's-a-string VM. Debugging clearly wasn't on the list of Useful Activities which the shell was meant to support. "rm: Is a directory". Gotta love that. Of course people write huge shell scripts. One excuse is that they want to modify env vars in the user's shell, and "only a shell script can do that" (wrong – you can use eval `sane-prog` instead of source insane-shell-script). A particularly awesome kind of shell script is the multi-kilobyte one-liner (find | grep | awk | grep -v | fuck-off-and-die).

I'll tell you why it happens. When you write code in a full-featured programming language, clearly you can do a lot of useful things. Because, like, everybody can. So the job has to be quite special to give you satisfaction; if the task is prosaic, and most of them are, there's little pride you're going to feel. But if the language is crippled, it's a whole different matter. "Look, a loop using templates!" Trivial stuff becomes an achievement, which feels good. I like feeling good. Templates are powerful! What do you mean by "solving a non-problem?" Of course I'm solving real problems! How else are you going to do compile-time loops in C++? How else are you going to modify env vars of the parent shell?! I'm using my proficiency with my tools and knowledge of their advanced features to solve problems! Damn, I'm good!

By the way, here's another entry in The Modern Software Industry Dictionary:


An attribute of programming environments or their individual features, most often Turing tar pits. A feature is "powerful" when at least one of the following holds:

  1. It can be used to implement something trivial in an pointlessly complicated way.
  2. It can cause a lot of damage.

Seriously, it seems like 85% percents of the contexts where something is called "powerful", it really means "useless and dangerous". Unlike most entries in the Modern Software Industry Dictionary, I don't consider this word a meaningless cheerleader noise. I think it actually carries semantics, making it a pretty good warning sign.

Back to our subject. A Turing tar pit deployed on a massive scale has two effects on programmers who got addicted to it:

  1. They waste an awful lot of time (ab)using it. Pretty obvious? Wait, there's more!
  2. They come to think that the sort of work they're used to accomplish with a Turing tar pit should always be done using a Turing tar pit. And this is just depressing. It really is.

Lisp-style macros, D-style mixins and code generation using DSL compilers are some ways to do compile-time things in a not entirely brain-crippled fashion. You know, you can actually concatenate two strings, which is unimaginable luxury in the world of C++ templates. People are actually afraid of these things. These people aren't cowards, mind you. These are the same people who'd fearlessly delve into the darkest caves of template metaprogramming. Sure, it's "non-trivial", but sometimes you need the Powerful Features to get your job done! But a full-blown programming language for compile-time work? Are you kidding? That is just too dangerous and unmaintainable! And anyway, you can do everything with templates – they're Turing-complete! Neat, ain't it?!

Alternatives to TeX... I'm bad at this, I really am, so you won't get a detailed rant on this subject. Let's just say that WYSIWYG is underestimated by many programmers, and extending a wiki engine, even one written in PHP, beats extending TeX hands down. This isn't a first-hand evidence, just generic Turing-tar-pit intuition. This is the part where you can tell me that I'm a moron and get away without a symmetrical remark. In particular, TeX seems to have awfully good back-ends; I don't think it can possibly justify heavy usage of its front-end macro facilities, but, um, everything is possible.

Scripting. Back to yosefk's-perceived-competence-land. When people hear about a new language, and they're told that it's a scripting language, not only don't they treat it seriously, they insist on emulating a Turing tar pit in it. They call system() and pass it incomprehensible 300-character pipelines. They write everything in one big bulk, without using functions or classes. They ignore data structures and regular expressions and call awk when they need them the way they'd do in a shell script. From Python or Ruby or Perl. This is how you write scripts, you know.

Interesting, isn't it? I find it fascinating. I think that software is to wetware what leaves are to trunks; to figure out the leaves, you have to saw through the trunk and see what's inside, or something. I also think that crappy software isn't necessarily written by dumb people, although that helps. I think that the attitude and the state of mind is at least as important as raw aptitude, much like the direction at which you aim a cannon isn't less important than its range. I'll definitely share those thoughts with you, as well as many others, but that will have to wait for another time. It's been a pleasure having you with us. Good night.