Thompson: I don’t know. I think it’s losing at Google. Now there are more people who don’t like it than like it.

Seibel: And they switch to Java?

Thompson: I don’t know. There’s almost no replacement for it. They complain, but they don’t switch. Graduate students coming out—the people who are hired by Google—know it. So it’s hard to do anything else. That’s the reason it keeps going—it saves a tremendous amount of education, reeducation. It gets people productive faster.

Seibel: Are there other languages that you enjoy, or have enjoyed, programming in?

Thompson: All of the funny languages at one point I’ve taken a step in. Like for solving equations and stuff: Maple and Macsyma, things like that. For strings, SNOBOL. Anyway, I’ve played with dozens and dozens of languages, if they do something that’s interesting.

Seibel: And are there development tools that just make you happy to program?

Thompson: I love yacc. I just love yacc. It just does exactly what you want done. Its complement, Lex, is horrible. It does nothing you want done.

Seibel: Do you use it anyway or do you write your lexers by hand?

Thompson: I write my lexers by hand. Much easier.

Seibel: Have you ever done any literate programming, a la Donald Knuth?

Thompson: No. It’s a great idea, but it’s almost impossible to do in practice.

Seibel: Why?

Thompson: It’s two representations of the same program that are often out of phase and conflict with each other. And there’s no way to resolve it. If something is written well in a programming language, then it’s readable. It suffices. The comments don’t need to be that parallel. The comments are maybe for algorithms, or if you do something tricky it’d probably be more in the form of a warning or something. I’m not a big, gross comment kind of guy. It’s legendary.

Seibel: When I interviewed him, Knuth said the key to technical writing is to say everything twice in complementary ways. So I think he sees that as a feature of literate programming, not a bug.

Thompson: Well if you have two ways, one of them is real: what the machine executes. One of them is not. Only if one is massively more brief way than the other is it worthwhile. If it’s the same volume, you read the one that works. If one is much more terse, much less precise, and you can get out of it what you need, then that’s great. But very often you can’t get out of it what you need—you really need the nitty-gritty and then you go to the other. Depending on what you’re after, you read one or the other. But to try to have microscopic descriptions of an algorithm, one in the programming language and one in English—maybe Knuth can do it, but I can’t.

Seibel: Have you ever read any of his literate programs?

Thompson: Just his stuff in the early papers. Nothing recent.

Seibel: And are there books that you think are particularly important—that either were important to you or that you would recommend people to read?

Thompson: I don’t read beginning programming books, so I have trouble recommending such things. If I have to learn a new language or something I’ll try to find a book. I prefer much denser books that just give me the syntax and semantics rather than chatting me up and telling me what’s good style and what’s bad style.

When I taught, I would have to select a textbook for my course and would read all of the textbooks in the area and have to make a selection. So at two points in time, I knew the basic literature for those courses. But outside that I don’t read.

Seibel: When you were inventing Unix you had your plan to do the four pieces that would actually give you an operating system. Then your wife and kids went away, leaving you free to hack for a month. I assume you put in some long hours in that month. Why do we do that? Is it necessary? Is it just because it’s fun?

Thompson: You do it when you’re driven. I don’t think I could have not done it. The other thing is when the wife and kid are around you have this synchronizing to a 24-hour cycle. When they go away, I don’t have a 24-hour cycle. There’s nothing that keeps me and the sun together. And so I typically sleep on a 27- or 28-hour cycle, sleeping 6 hours. So I drift. When I get to sleep until I wake up I’m in better shape to work than if I get to sleep and get up when the kid starts screaming.

Seibel: So that’s when you’re driven by a project and you wake up wanting to get to the computer to start writing more code. But people also work long hours because we have this idea that we’ve got to get this product out the door and the way to do it is for everyone to work 80, 100 hours a week.

Thompson: That generates burnout. Excitement programming, I never ever felt stress. I’ve been in other situations too where deadlines—external deadlines—generate stress. That’s not fun; I don’t like that.

Seibel: You burn out at the end, which is obviously bad, but in terms of getting things done in the short term, does it work?

Thompson: Usually you’re in a position where such a thing is continual. That as soon as that deadline is over another one starts coming up over the horizon. If you’re constantly under deadlines like that, then the next one you’ll have less enthusiasm and pretty soon you just can’t live like that. I can’t.

Seibel: Tied up with trying to meet deadlines is being able to estimate how long things are going to take. Can you estimate how long it’s going to take to write a given piece of code?

Thompson: It depends on whether I’m writing it for me or writing it for production. I can if I’m writing for me. I can live with the quirks. I can not do the extra ten percent. I can avoid the gaping holes that I know are in there. Things like that. I can produce it and then clean it up at leisure and still use it. Maybe that’s a different definition of finished. But if you’re doing it for production then usually there are other people involved and coordination—I can’t estimate that.

Seibel: In one 1999 interview you said you didn’t think much of Linux, and got the Linux guys all up in arms. What do you think of it now about a decade later, and it’s taking over the world?

Thompson: It’s much more reliable—there’s no doubt about that. And I’ve looked at the code occasionally. I don’t look at it as much as I used to. I used to, for Plan 9. They were always ahead of us—they just had massively more resources to deal with hardware. So when we’d run across a piece of hardware, I’d look at the Linux drivers for it and write Plan 9 drivers for it. Now I have no reason to look at it. I run Linux. And I occasionally look at code, but rarely, so I can’t really tell whether the quality has gotten better or not. But certainly the reliability has gotten better.

Seibel: Do you ever read code just for fun?

Thompson: In the past I used to; less so now. When I first came here I did it just to try and get the feel of the place. You’ve got to. There’s so much unsaid that you’ve got to know.

Seibel: Would you pick a program and completely understand it, or were you just sort of looking for how do they do things around here?

Thompson: A little bit of both. I’d certainly try to pick the big libraries at first. I’d look at the main programs of some of the things. The programming style here at Google is so bizarre. They take a subroutine call, package it as an RPC, and store it somewhere static. Which means anybody can call it at any time for any reason. And then they call generic listening kind of code and somebody somewhere gets a message, goes off and finds that, and makes that subroutine call.

Seibel: So that’s a mechanism for distributed computation.