Given GNU's desire to replicate Unix, I think Bison was inevitable. I am bemused that some GNU people are so irritated that GNU's contribution to Linux is not recognized, but yet they have failed to recognize their debt to those of us who worked on Unix...
In your opinion, what lasting legacy has YACC brought to language development?
YACC made it possible for many people who were not language experts to make little languages (also called domain-specific languages) to improve their productivity. Also, the design style of YACC - base the program on solid theory, implement the theory well, and leave lots of escape hatches for the things you want to do that don't fit the theory - was something many Unix utilities embodied. It was part of the atmosphere in those days, and this design style has persisted in most of my work since then.
Where do you envisage the future of parser generators lying?
The ideas and techniques underlying YACC are fundamental and have application in many areas of computer science and engineering. One application I think is promising is using compiler-design techniques to design GUIs - I think GUI designers are still writing GUIs in the equivalent of assembly language, and interfaces have become too complicated for that to work any more.
What are you proudest of in terms of YACC's development and use?
I think computing is a service profession. I am happiest when the programs that I have written (YACC, Lint, the Portable C Compiler) are useful to others. In this regard, the contribution YACC made to the spread of Unix and C is what I'm proudest of.
Where do you see computer programming languages heading in the future, particularly in the next 5 to 20 years?
I like constraint languages, particularly because I think they can easily adapt to parallel hardware.
Do you have any advice for up-and-coming programmers?
You can't rewrite a program too many times, especially if you make sure it gets smaller and faster each time. I've seen over and over that if something gets an order of magnitude faster, it becomes qualitatively different. And if it is two orders of magnitude faster, it becomes amazing. Consider what Google would be like if queries took 25 seconds to be answered...
One more piece of advice-take a theoretician to lunch...