## The history of Calc

I’m taking some time off from cramming my KMD2004 project to write a

review of Emacs 22 prerelease for Don Marti. It’s a great excuse to

look at all the cool new features I’d been taking for granted in my

Emacs CVS.

I love the stories people tell through their code and their

documentation! For example, take Calc mode. You’d expect it to be a

simple desk calculator, right? No, it can do “arithmetic on rational

numbers, complex numbers (rectangular and polar), error forms with

standard deviations, open and closed intervals, vectors and matrices,

dates and times, infinities, sets, quantities with units, and

algebraic formulas.” It has tons of other features, too.

How did a calculator get so big, the way all Emacs features seem to

grow and grow and grow? Check out the History and Acknowledgements

section of the info manual for Calc. Here’s the story from David

Gillespie in the manual:

Calc was originally started as a two-week project to occupy a lull in

the author’s schedule. Basically, a friend asked if I remembered the

value of `2^32′. I didn’t offhand, but I said, “that’s easy, just call

up an `xcalc’.” `Xcalc’ duly reported that the answer to our question

was `4.294967e+09’—with no way to see the full ten digits even though

we knew they were there in the program’s memory! I was so annoyed, I

vowed to write a calculator of my own, once and for all.I chose Emacs Lisp, a) because I had always been curious about it

and b) because, being only a text editor extension language after all,

Emacs Lisp would surely reach its limits long before the project got

too far out of hand.To make a long story short, Emacs Lisp turned out to be a

distressingly solid implementation of Lisp, and the humble task of

calculating turned out to be more open-ended than one might have

expected.Emacs Lisp doesn’t have built-in floating point math, so it had to be

simulated in software. In fact, Emacs integers will only comfortably

fit six decimal digits or so—not enough for a decent calculator. So I

had to write my own high-precision integer code as well, and once I had

this I figured that arbitrary-size integers were just as easy as large

integers. Arbitrary floating-point precision was the logical next step.

Also, since the large integer arithmetic was there anyway it seemed only

fair to give the user direct access to it, which in turn made it

practical to support fractions as well as floats. All these features

inspired me to look around for other data types that might be worth

having.Around this time, my friend Rick Koshi showed me his nifty new HP-28

calculator. It allowed the user to manipulate formulas as well as

numerical quantities, and it could also operate on matrices. I decided

that these would be good for Calc to have, too. And once things had

gone this far, I figured I might as well take a look at serious algebra

systems for further ideas. Since these systems did far more than I

could ever hope to implement, I decided to focus on rewrite rules and

other programming features so that users could implement what they

needed for themselves.Rick complained that matrices were hard to read, so I put in code to

format them in a 2D style. Once these routines were in place, Big mode

was obligatory. Gee, what other language modes would be useful?Scott Hemphill and Allen Knutson, two friends with a strong

mathematical bent, contributed ideas and algorithms for a number of

Calc features including modulo forms, primality testing, and

float-to-fraction conversion.Units were added at the eager insistence of Mass Sivilotti. Later,

Ulrich Mueller at CERN and Przemek Klosowski at NIST provided invaluable

expert assistance with the units table. As far as I can remember, the

idea of using algebraic formulas and variables to represent units dates

back to an ancient article in Byte magazine about muMath, an early

algebra system for microcomputers.Many people have contributed to Calc by reporting bugs and suggesting

features, large and small. A few deserve special mention: Tim Peters,

who helped develop the ideas that led to the selection commands, rewrite

rules, and many other algebra features; Francois Pinard, who

contributed an early prototype of the Calc Summary appendix as well as

providing valuable suggestions in many other areas of Calc; Carl Witty,

whose eagle eyes discovered many typographical and factual errors in

the Calc manual; Tim Kay, who drove the development of Embedded mode;

Ove Ewerlid, who made many suggestions relating to the algebra commands

and contributed some code for polynomial operations; Randal Schwartz,

who suggested the `calc-eval’ function; Robert J. Chassell, who

suggested the Calc Tutorial and exercises; and Juha Sarlin, who first

worked out how to split Calc into quickly-loading parts. Bob Weiner

helped immensely with the Lucid Emacs port.Among the books used in the development of Calc were Knuth’s _Art of

Computer Programming_ (especially volume II, _Seminumerical

Algorithms_); _Numerical Recipes_ by Press, Flannery, Teukolsky, and

Vetterling; Bevington’s _Data Reduction and Error Analysis for the

Physical Sciences_; _Concrete Mathematics_ by Graham, Knuth, and

Patashnik; Steele’s _Common Lisp, the Language_; the _CRC Standard Math

Tables_ (William H. Beyer, ed.); and Abramowitz and Stegun’s venerable

_Handbook of Mathematical Functions_. Also, of course, Calc could not

have been written without the excellent _GNU Emacs Lisp Reference

Manual_, by Bil Lewis and Dan LaLiberte.Final thanks go to Richard Stallman, without whose fine

implementations of the Emacs editor, language, and environment, Calc

would have been finished in two weeks.

I’ve had a lot of these two week projects. I wasn’t supposed to get

hooked on Planner. It was just supposed to be one of the components of

my fourth-year undergrad project. It turned into a way of life and my

main open source project for almost three years.

Most people look at Emacs and they see an editor with way, way, way

too many features. How many people need to do in-line matrix

calculations, anyway? I might never use it (then again, who knows?),

but I think it’s terrific that someone just sat down one day and put

it in. When I look at Emacs, I see more than a text editor. I see a

community of hackers and a tradition of tinkerers. It’s awesome. =)

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History and Acknowledgements

Random Emacs symbol: enable-kinsoku – Variable: *Non-nil means enable “kinsoku” processing on filling paragraphs.