Just over eleven years ago I was faced with selecting a topic for my thesis. At the time, I was a student at the Massachusetts Institute of Technology and was working on my bachelor's degree in Computer Science and Engineering. One of the degree requirements was a thesis, and you can't have a thesis without a topic.

During my four years at M.I.T., a new type of text editor had come into being and widespread use. This type of text editor was called "Emacs," and it was a major step forward in many ways. Implementations of this type of editor were appearing on many computer systems. Some people even used an implementation as the basis for their thesis. I took a different tack. The idea that I settled on for my thesis was a description of the technology that underlies all text editors, but with a special emphasis on Emacs-type editors. The thesis was written and published as a technical memo (Finseth 1980).

* * *

Ten years later, I was reading the USENET News news group Comp.editors, one of the many facets of that worldwide electronic bulletin board. A discussion thread had started up in which both sides of the discussion were citing my thesis as the authority in the field. Further inquiries (not by me: I was just reading along) showed that no one in that group was aware of any other document that described general text-editing technology.

My thesis was ten years old: it predated most personal computers and workstations. There had even been a chapter in an early draft that attempted to prove that it was not possible to implement an Emacs-type text editor on a small computer. (I invented a way, threw out the chapter, and with some friends started a software company to market such an editor. Oh well.) It was clearly time for a complete rewrite, and that rewrite is what you are reading now.

If you don't have a copy of my thesis (or the Technical Memo: the two have identical content), you won't miss anything. This book has all of the information from the earlier document, and is now updated. It also has a whole lot more. Every part has been completely rewritten and expanded, and major sections have been added.

As with my thesis, this book is written in an informal, almost chatty style. It is addressed directly to "you," who are assumed to care about how text editors are implemented. Be warned, however, that it also contains opinions about the "right" and "wrong" way of doing things and that these opinions hold that many of the current directions and trends are -- shall we say? -- not the "right" way. You should keep in mind that you should not accept everything said in here as the gospel truth, but understand why I say what I say and make your own informed judgment.

This book is addressed to anyone who implements large software systems or who wants to know the considerations that go into such systems. It focuses around text editors. Although not required, an understanding of programming will be helpful.

Questions to Probe Your Understanding

Each chapter ends with a set of questions and problems designed to probe your understanding of the material that was just presented. And, true to the Socratic method, some of these questions also introduce new material. The level of difficulty of the questions ranges from very easy to quite difficult, and each question is labelled to help you gauge how much effort is required. Just as with most programming issues, most questions have no single correct answer.


would like to thank those people who helped me in various ways:

Owen "Ted" Anderson
Joe Austin
Jeff Brown
Bernard Greenberg
Brian Hess
Mike Kazar
Richard Kovalcik
Scott Layson
Jason Linhart
David Moon
Robert Nathaniel
Lee Parks
Jeffrey Schiller
Richard Stallman
Seth Steinberg
Peter Steinmetz
Liba Svobodova
Daniel Weinreb

lus, of course, all of those people that I have left out. Special thanks to my wife Ann and daughter Kari, who put up with my typing away all the time.

Craig A. Finseth
St. Paul, Minnesota
February 1991

Copyright 1999 by Craig A. Finseth.

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