TUGboat, Volume 26 (2005), No. 3 183

Interview with Donald E. Knuth

Gianluca Pignalberi

Abstract

A prime number of questions to the Professor Emer-itus of the Art of Computer Programming.

Introduction

The typesetting of Free Software Magazine is en-tirely TEX-based, so that process uses the programthat Prof. Donald Knuth designed some 30 yearsago. Since then the TEX project has generated manyoffshoots (i.e., LATEX, ConTEXt, Ω, and others).

In May 2005 I had the chance and the honor tointerrupt Prof. Knuth’s activity and interview himfor Free Software Magazine. I’m proud, as a jour-nalist and FSM TEXnician, to see it republished inTUGboat.

GP: Donald E. Knuth, Professor Emeritus of the Artof Computer Programming, Professor of (Concrete)Mathematics, creator of TEX and METAFONT, au-thor of several fantastic books (such as Computers& Typesetting, The Art of Computer Programming,Concrete Mathematics) and articles, recipient of theTuring Award, Kyoto Prize, and other importantawards; fellow of the Royal Society (I could keep go-ing). Is there anything you feel you have wanted tomaster and haven’t? If so, why?

DEK: Thanks for your kind words, but really I’mconstantly trying to learn new things in hopes that Ican then help teach them to others. I also wish I wasable to understand non-English languages withoutso much difficulty; I’m often limited by my linguisticincompetence, and I want to understand people fromother cultures and other eras.

GP: Your algorithms are well known and well docu-mented (I’ll only quote, for brevity’s sake, the Knuth-Morris-Pratt String Matching algorithm), which al-lows everyone to use, study and improve upon themfreely. If it wasn’t clear through your actions, in aninterview with Dr. Dobb’s Journal, you stated youropinion about software patents, which are forcingpeople to pay fees if they either want to use or mod-ify patented algorithms. Has your opinion on soft-ware patents changed or strengthened? If so, how?And how do you view the EU Parliament’s wishesto adopt software patent laws?

Editor’s note: This article was originally published in TheFree Software Magazine, issue 7 (2005), and is reprinted bykind permission of the interviewer and editor.

DEK: I mention patents in several parts of The Artof Computer Programming. For example, when dis-cussing one of the first sorting methods to be patent-ed, I say this:

Alas, we have reached the end of the era whenthe joy of discovering a new algorithm wassatisfaction enough! Fortunately the oscillat-ing sort isn’t especially good; let’s hope thatcommunity-minded folks who invent the bestalgorithms continue to make their ideas freelyavailable.

I don’t have time to follow current developments inthe patent scene; but I fear that things continue toget worse. I don’t think I would have been able tocreate TEX if the present climate had existed in the1970s.

On my recent trip to Europe, people told methat the EU had wisely decided not to issue soft-ware patents. But a day or two before I left, some-body said the politicians in Brussels had suddenly

Figure 1: Prof. Knuth while reading one of themagazines typeset by his program TEX. Photoby Jill Knuth (a graduate of Flora Stone MatherCollege — another FSM).

184 TUGboat, Volume 26 (2005), No. 3

Figure 2: The portion of the paper where Knuthanswered question 2 of this interview. Please notethat he typographically quotes and typesets evenwhen writing by hand: the quotation from TAOCP

and the word TEX.

reversed that decision. I hope that isn’t true, be-cause I think today’s patent policies stifle innova-tion.

However, I am by no means an expert on suchthings; I’m just a scientist who writes about pro-gramming.

GP: So far you have written three volumes of TheArt of Computer Programming, are working on thefourth, are hoping to finish the fifth volume by 2010,and still plan to write volumes six and seven. Apartfrom the Selected papers series, are there any othertopics you feel you should write essays on, but donot have time for? If so, can you summarize whatsubject you would write on?

DEK: I’m making slow but steady progress on vol-umes 4 and 5. I also have many notes for volumes 6and 7, but those books deal with less fundamentaltopics and I might find that there is little need forthose books when I get to that point.

I fear about 20 years of work are needed beforeI can bring TAOCP to a successful conclusion; andI’m 67 years old now; so I fondly hope that I willremain healthy and able to do a good job even asI get older and more decrepit. Thankfully, at themoment I feel as good as ever.

If I have time for anything else I would like tocompose some music. Of course I don’t know if thatwould be successful; I would keep it to myself if itisn’t any good. Still, I get an urge every once inawhile to try, and computers are making such thingseasier.

GP: There are rumours that you started the TEXproject because you were tired of seeing your man-uscripts mistreated by the American MathematicalSociety. At the same time, you stated that you cre-ated it after seeing the proofs of your book The Artof Computer Programming. Please, tell our readersbriefly what made you decide to start the project,which tools you used, and how many people you hadat the core of the TEX team.

DEK: No, the math societies weren’t to blame forthe sorry state of typography in 1975. It was thefact that the printing industry had switched to newmethods, and the new methods were designed tobe fine for magazines and newspapers and novelsbut not for science. Scientists didn’t have any eco-nomic clout, so nobody cared if our books and pa-pers looked good or bad.

I tell the whole story in Chapter 1 of my bookDigital Typography, which of course is a book I hopeeverybody will read and enjoy.

The tools I used were home grown and becameknown as Literate Programming. I am enormouslybiased about Literate Programming, which is surelythe greatest thing since sliced bread. I continueto use it to write programs almost every day, andit helps me get efficient, robust, maintainable codemuch more successfully than any other way I know.Of course, I realize that other people might findother approaches more to their liking; but wow, Ilove the tools I’ve got now. I couldn’t have writtendifficult programs like the MMIX meta-simulator atall if I hadn’t had Literate Programming; the taskwould have been too difficult.

At the core of the TEX team I had assistantswho read the code I wrote, and who prepared printerdrivers and interfaces and ported to other systems.I had two students who invented algorithms for hy-phenation and line breaking. And I had many dozensof volunteers who met every Friday for several hoursto help me make decisions. But I wrote every lineof code myself.

TUGboat, Volume 26 (2005), No. 3 185

Chapter 10 of my book Literate Programmingexplains why I think a first-generation project likethis would have flopped if I had tried to delegate thework.

GP: Maybe you feel that some of today’s technolo-gies are still unsatisfactory. If you weren’t busy writ-ing your masterpieces, what technology would youtry to revolutionize and in what way?

DEK: Well, certainly I would try to work for worldpeace and justice. I tend to think of myself as acitizen of the world; I am pleasantly excited whenI see the world getting smaller and people of differ-ent cultures working together and respecting theirdifferences. Conversely I am distressed when I learnabout deep-seated hatred or when I see people ex-ploiting others or shoving them around pre-empt-ively.

In what way could the desired revolution comeabout? Who knows . . . but I suspect that “En-gineers Without Borders” are closer than anybodyelse to a working strategy by which geeks like mecould help.

GP: Thank you again for your precious time.

DEK: Thank you for posing excellent questions!

Copyright information

c© 2005 Gianluca PignalberiThis article is made available under the“Attribution-NonCommercial-NoDerivs”Creative Commons License 2.0, available fromhttp://creativecommons.org/licenses/by-nc-nd/2.0/.

Gianluca PignalberiVia del Pozzo, 3404010 Cori (LT)Italyg.pignalberi (at) freesoftwaremagazine.

com

http://www.freesoftwaremagazine.com/

contacts

Figure 3: Portrait of Donald E. Knuth byAlexandra Drofina. Commercial users shouldwrite to Yura Revich (revich@computerra.ru) forpermission.