23 January, 2009

What do programmers do?

Have you been ever asked what you do for work? I have, and it's always hard for me to answer: if I say I'm a computer programmer people immediately think I can fix their printer - or worse, they want me to build them a dating website for five hundred bucks.

The truth is that what we "computer scientists" do is more along the lines of what sorcerers do. Hal Abelson describes it really well:

Computational processes are abstract beings that inhabit computers. As they evolve, processes manipulate other abstract things called data. The evolution of a process is directed by a pattern of rules called a program. People create programs to direct processes. In effect, we conjure the spirits of the computer with our spells.

A computational process is indeed much like a sorcerer's idea of a spirit. It cannot be seen or touched. It is not composed of matter at all. However, it is very real. It can perform intellectual work. It can answer questions. It can affect the world by disbursing money at a bank or by controlling a robot arm in a factory. The programs we use to conjure processes are like a sorcerer's spells. They are carefully composed from symbolic expressions in arcane and esoteric programming languages that prescribe the tasks we want our processes to perform.

A computational process, in a correctly working computer, executes programs precisely and accurately. Thus, like the sorcerer's apprentice, novice programmers must learn to understand and to anticipate the consequences of their conjuring. Even small errors (usually called bugs or glitches) in programs can have complex and unanticipated consequences.

Fortunately, learning to program is considerably less dangerous than learning sorcery, because the spirits we deal with are conveniently contained in a secure way. Real-world programming, however, requires care, expertise, and wisdom. A small bug in a computer-aided design program, for example, can lead to the catastrophic collapse of an airplane or a dam or the self-destruction of an industrial robot.

Master software engineers have the ability to organize programs so that they can be reasonably sure that the resulting processes will perform the tasks intended. They can visualize the behavior of their systems in advance. They know how to structure programs so that unanticipated problems do not lead to catastrophic consequences, and when problems do arise, they can debug their programs. Well-designed computational systems, like well-designed automobiles or nuclear reactors, are designed in a modular manner, so that the parts can be constructed, replaced, and debugged separately.

Although I'm attributing the quote to Abelson, the text above comes from the book Structure and Interpretation of Computer Programs, written by Albeson, Sussman, and Sussman. The reason I'm attributing the quote to Albeson is because I first came across this by watching one of his MIT lectures on the same topic.

If you're interested in watching MIT's introductory "Structure and Interpretation of Computer Programs" class, you can find the videos here.

And now, go conjure some spirits!


Mike Murray said...

Awesome! I'm more like Harry Potter and Merlin than I thought.

I ususally tell people I am a "Software Engineer". They either go "Oh, wow!" or they just look at me like "Huh?" If the response is the latter, then I usually resort to the clarification that I'm a "Programmer."

I had one neighbor say, "Oh wow, you have like a real occupation!" I live in a pretty young ward where I guess everyone is still playing "House" or something (a huge majority is like 5 years of marriage and under). I suppose they're all students that go do Alarm Sales during the summer.

Esteban Araya said...


Yeah, I stopped telling people I'm a software engineer long time ago...

What your neighbor said makes me laugh: not only do you have an occupation; you get to do something you actually LOVE doing. Isn't that awesome?

BTW, I've got a post on "software engineering" coming up: I hate the term; I think what we do is nothing like engineering. But like I said, you'll hear more on that later.

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