And so to me reading source materials is great enrichment for my own lifeand creativity.

I was unable to pass that on to any of my students. There are people alivenow in computer science who are doing this well—a few. But I could counton the fingers of one hand the people who love source materials the way Ido.

I’ve got lots of collections of source code. I have compilers, the Digitekcompilers from the 1960s were written in a very interesting way. They hadtheir own language and they used identifiers that were 30 characters longbut very descriptive, and their compilers ran circles around the competitionat the time—this company made the state-of-the-art compilers of 1963 or’64.

And I’ve got Dijkstra’s source code for the THE operating system. I haven’tread that. I’ve just skimmed it so far but I collected it because I’m sure itwould be interesting to read if I had time.

One time I broke my arm—fell off a bike—and I had a month where Icouldn’t do anything much, so I read source code that I had heard had someclever ideas in it that hadn’t been documented. I think those were allextremely important experiences for me.

Seibel: How do you tackle reading source code? Even reading something ina programming language you already know is a tricky problem.

Knuth: But it’s really worth it for what it builds in your brain. So how do Ido it? There was a machine called the Bunker Ramo 300 and somebody toldme that the Fortran compiler for this machine was really amazingly fast, butnobody had any idea why it worked. I got a copy of the source-code listingfor it. I didn’t have a manual for the machine, so I wasn’t even sure what themachine language was.

But I took it as an interesting challenge. I could figure out BEGIN and then Iwould start to decode. The operation codes had some two-lettermnemonics and so I could start to figure out “This probably was a loadinstruction, this probably was a branch.” And I knew it was a Fortrancompiler, so at some point it looked at column seven of a card, and that waswhere it would tell if it was a comment or not.

After three hours I had figured out a little bit about the machine. Then Ifound these big, branching tables. So it was a puzzle and I kept just makinglittle charts like I’m working at a security agency trying to decode a secretcode. But I knew it worked and I knew it was a Fortran compiler—it wasn’tencrypted in the sense that it was intentionally obscure; it was only in codebecause I hadn’t gotten the manual for the machine.

Eventually I was able to figure out why this compiler was so fast.Unfortunately it wasn’t because the algorithms were brilliant; it was justbecause they had used unstructured programming and hand optimized thecode to the hilt.

It was just basically the way you solve some kind of an unknown puzzle—maketables and charts and get a little more information here and make a hypothesis.In general when I’m reading a technical paper, it’s the same challenge. I’mtrying to get into the author’s mind, trying to figure out what the concept is.The more you learn to read other people’s stuff, the more able you are toinvent your own in the future, it seems to me.

We ought to publish code. The Lions Book is available. And Bill Atkinson’sprograms are now publicly available thanks to Apple, and it won’t be toolong before we’ll be able to read that. That’s well-documented code withlots of pioneering graphics algorithms in it.

Seibel: Certainly with open source there’s a lot more code out there toread than there use to be.

Knuth: Yeah, that’s right. But the more varieties of different kinds ofnotations are still useful—don’t only read the people who code like you.

The Art of Computer Programming, Donald Knuth (Addison-Wesley, 1997)

Beautiful Code: Leading Programmers Explain How They Think, AndyOram, Greg Wilson (eds.) (O’Reilly, 2007)

Byte, Vol. 6, No. 8, “Smalltalk issue,” August 1981

Code Complete, Steve McConnell (Microsoft Press, 1993)

Compiling with Continuations, Andrew W. Appel (Cambridge UniversityPress, 1992)

The Design and Analysis of Computer Algorithms, Alfred V. Aho, John E.Hopcroft, and Jeffrey D. Ullman (Addison-Wesley, 1974)

Design Patterns: Elements of Reusable Object-Oriented Software, EricGamma, Richard Helf, Ralph Johnson, and John M. Vlissides (Addison-Wesley Professional, 1994)

A Discipline of Programming, Edsger W. Dijkstra (Prentice Hall, Inc., 1976)

Effective Java, Joshua Bloch (Prentice Hall, 2008)

The Elements of Programming Style, Brian Kernighan and P.J. Plauger(Computing McGraw-Hill, 1978)

Elements of Style, William Strunk and E.B. White (Longman, 1999)

Expert C Programming, Peter van der Linden (Prentice Hall PTR, 1994)

Founders at Work, Jessica Livingston (Apress, 2007)

Hacker’s Delight, Henry S. Warren (Addison-Wesley, 2002)

Higher-Order Perl, Mark Jason Dominus (Morgan Kaufmann, 2005)

Java Concurrency in Practice, Brian Goetz, Tim Peierls, Joshua Bloch,Joseph Bowbeer, David Holmes, and Doug Lea (Addison-Wesley, 2006)

Java Puzzlers: Traps, Pitfalls, and Corner Cases, Joshua Bloch and NeilGafter (Addison-Wesley, 2005)

The Lisp 1.5 Programmer’s Manual, John McCarthy (MIT Press, 1962)

Literate Programming, Donald Knuth (Center for the Study of Languageand Information, 1992)

Machine Intelligence 1, N.L. Collins and Donald Michie (eds.) (Oliver andBoyd, 1967)

Machine Intelligence 2, Ella Dale and Donald Michie (eds.) (Oliver andBoyd, 1968)

Machine Intelligence 3, Donald Michie (ed.) (Edinburgh University Press,1968)

Machine Intelligence 4, Bernard Meltzer and Donald Michie (eds.)(Edinburgh University Press, 1969)

Magic House of Numbers, Irving Adler (HarperCollins, 1974)

META II a Syntax-Oriented Compiler Writing Language, D.V. Schorre inProceedings of the 1964 19th ACM national conference, (ACM, 1964)

Mindstorms: Children, Computers, and Powerful Ideas, Seymour A. Papert(Basic Books, 1993)

The Mythical Man-Month: Essays on Software Engineering, Frederick P.Brooks (Addison-Wesley Professional, 1995)

Principles of Compiler Design, Alfred Aho and Jeffrey Ullman (Addison-Wesley, 1977)

“Proof of a Program: FIND”, C.A.R. Hoare in Communications of the ACM,Vol. 14, Issue 1 (ACM, 1971)

Programming Pearls, Jon Bentley (ACM Press, 1999)

Purely Functional Data Structures, Chris Okasaki (Cambridge UniversityPress, 2008)

A Retargetable C Compiler: Design and Implementation, David Hanson andChristopher Fraser (Addison-Wesley Professional, 1995)

Smalltalk-80: The Interactive Programming Environment, Adele Goldberg(Addison-Wesley, 1983)

Smalltalk-80: The Language & Its Implementation, David Robson and AdeleGoldberg (Addison-Wesley, 1983)

Structure and Interpretation of Computer Programs, Harold Abelson andGerald Jay Sussman (MIT Press, 1996)

TeX: The Program, Donald Knuth (Addison-Wesley, 1986)

The Programming Language LISP: Its Operation and Applications, EdmundBerkeley and Daniel Bobrow, eds. (MIT Press, 1966)

The Psychology of Computer Programming: Silver Anniversary Edition,Gerald Weinberg (Dorset House, 1998)

The TeXbook, Donald Knuth (Addison-Wesley Professional, 1986)

Writers at Work: The Paris Review Interviews, Malcolm Cowley (Penguin,1977)

Zen and the Art of Motorcycle Maintenance: An Inquiry into Values, RobertPirsig (Bantam, 1984)