In 2002 Deutsch quit work on Ghostscript in order to study musical composition.Today he is more likely to be working on a new musical composition than on anew program, but still can’t resist the urge to hack every now and then, mostly ona musical score editor of his own devising.

Among the topics we covered in our conversation were the deep problems he seeswith any computer language that includes the notion of a pointer or a reference,why software should be treated as a capital asset rather than an expense, andwhy he ultimately retired from professional programming.

Seibel: How did you start programming?

Deutsch: I started programming by accident when I was 11. My dadbrought home some memo from the Cambridge Electron Accelerator,which was being built at the time. There was a group that did designcomputations and some memo of theirs accidentally found its way to him. Isaw it lying around his office and it had some computer code in it and therewas something about it that caught my imagination.

It turned out the memo was actually an addendum to another memo so Iasked him if he could lay his hands on the original memo. He brought thathome and I said, “Gee, this stuff is really interesting.” I think I might actuallyhave asked him if I could meet the guy who had written the memos. Wemet. I don’t really remember the details any more—this was 50 years ago.Somehow I got to write a little bit of code for one of the design calculationsfor the Cambridge Electron Accelerator. That’s how I got started.

Seibel: So that was when you were eleven. By 14 or 15 you were playingon the PDP-1s at MIT, where your dad was a professor.

Deutsch: When I was 14, I found my way to the TX-0 and to the PDP-1 shortlythereafter. I remember getting a hold of a copy of the Lisp 1.5 programmers’manual. I don’t remember how. It was a very early version—it was actuallymimeographed—the old purple ink. There was something about Lisp that caught myimagination. I’ve always had a kind of mathematical bent, and Lisp just seemedsort of cool. I wanted to have one to play with and I couldn’t get my hands onthe Building 26 mainframe. So I did my Lisp implementation on the PDP-1.

Seibel: Do you remember at all how you designed your PDP-1 Lisp?

Deutsch: I’m smiling because the program was so small. Have you seen thelisting? It’s only a few hundred lines of assembler.

Seibel: I’ve seen it; I didn’t try to understand it. Was it just a matter oftransliterating the thing in the 1.5 manual into assembly?

Deutsch: No, no, no. All that was in the 1.5 manual was the interpreter. Ihad to write a reader and tokenizer and I had to design the data structuresand all that stuff. My recollection was that I did that the way I actually havedone most of my programming, which is to do the data structures first.When I was young enough that my intuition would point me in the rightdirection—I won’t say infallibly, but close enough—that was a really goodapproach.

In the last couple of years I’ve noticed that I’ve gotten rusty—my intuitiondoesn’t work so well anymore. I’ve been doing a substantial project off andon for several years now to do a good open-source music score editor. I’vebeen fiddling with that off and on for several years now and I find that lettingmy intuition steer me to the right data structures and then just writingeverything out from there just doesn’t work anymore.

Seibel: Do you think your intuition is actually worse or did you used tohave more stamina for making it work even if your intuition was actually abit off?

Deutsch: I think it’s some of each but I think it’s more the former. I thinkwhat intuition is, really, is an unconscious process for synthesizing a solutionout of a large amount of data. And as I’ve gotten further and further awayfrom being immersed in the stuff of software, the data that goes into thatsynthesis has become less and less accessible.

I’ve heard it said that to be a master at something you have to have, prettymuch at your command, something like 20,000 specific cases. What’shappened is the 20,000 specific cases of software design that passed in frontof my face in my 45 years in the industry are just gradually becoming lessand less accessible, the way memories do. I think that’s pretty much what’sgoing on.

Seibel: Do you remember what it was about programming that drew youin?

Deutsch: With the benefit of 50 years of hindsight, I can see that I havealways been drawn to systems of denotative symbols—languages. Not onlylanguages of discourse—human languages—but languages in whichutterances have effects. Programming languages certainly fall right into thatcategory.

I think that also has something to do with why the career that I’ve switchedinto is musical composition. Music is a language, or a family of languages, butwhat you say in those languages not only has denotation, maybe, but it alsoit has effects on people. Music is kind of interesting because on thespectrum of formality it falls between natural languages and computerlanguages. It’s more formal and structured than a natural language, but itdoesn’t have nearly the structure or formality of a computer language. That,I think, may have to do with why I went into music and not poetry. I thinkpoetry is not structured enough for me.

But the short answer really is, I just gravitated to this stuff right away.

Seibel: Do you remember the first interesting program you wrote?

Deutsch: The first program that I wrote because the content interestedme was actually the second program that I wrote. The first program I wrotewas some piece of calculation having to do with the Cambridge ElectronAccelerator. The second program was a floating-point-output-formattingprogram.

Seibel: Which is a pretty hairy problem.

Deutsch: Well it is on a binary machine. It’s not a hairy problem on adecimal machine, and I was working on a decimal machine. You just slide thestring around and decide where to put the decimal point. You have todecide whether to use the E or F format. But in those days, everything wasa lot harder—I was writing in assembly language on a batch-processingmachine—so this was not a trivial problem. It wasn’t a hard problem but itwasn’t a trivial one. That was the first program that I wrote because Iwanted to.

Seibel: So you were hanging out at MIT during high school and then youwent to Berkeley for college. Did you want to escape the East Coast?

Deutsch: Sort of. I realized that it would be really good for me to go tosomeplace that was far away from my parents. The three places that Iconsidered seriously were, I think it was University of Rochester, Universityof Chicago, and Berkeley. That was a no-brainer—only one of the three hasreasonable weather. So that’s how I ended up at Berkeley. And it was oneof the best things that ever happened in my life.

I was at Berkeley and I found Project Genie pretty quickly after I arrived andstayed with that project until—well there was Project Genie and then therewas Berkeley Computer Corporation and then there was Xerox.

Seibel: Presumably at Berkeley you started working on bigger projects thanyour PDP-1 Lisp implementation.

Deutsch: Oh, yeah. Considerably larger projects at Project Genie. To beginwith I wrote pretty much the whole operating-system kernel. The kernelwas probably pushing 10,000 lines.

Seibel: How did that change—an order-of-magnitude difference in size—changeyour design process?

Deutsch: I’m trying to remember what was in the kernel. It was still a smallenough program that I could approach it as a whole. There were obviouslyfunctional divisions. I know I had a clear mental model of which sections ofthe program were allowed to interact with which of the key data structures.But in fact there weren’t very damn many data structures. There was aprocess table; there were ready lists. There were I/O buffers and there wassome stuff for keeping track of virtual memory. And then there was an openfile table, per process. But the descriptions of all the system data structuresprobably could have fit on, in terms of C struct definitions, probably couldhave fit on two pages. So we’re not talking about a complicated system.