Chapter 9: Dividing and Conquering Using Procedures and Macros to Battle Complexity

Programming in Martian

There is a computer language called APL (an acronym for A Programming Language, how clever) that has more than a little Martian in it. APL was the first computer language I learned (on a major IBM mainframe), and when I learned it, I learned a little more than just APL.

APL uses a very compact notation, with dozens of odd little symbols, each of which is capable of some astonishing power such as matrix inversion. You can do more in one line of APL than you can in one line of anything else I have learned since. The combination of the strange symbol set and the compact notation makes it very hard to read and remember what a line of code in APL actually does.

So it was in 1977. Having mastered (or so I thought) the whole library of symbols, I set out to write a text formatter program. The program would justify right and left, center headers, and do a few other things of a sort that we take for granted today but which were very exotic in the seventies.

The program grew over a period of a week to about 600 lines of squirmy little APL symbols. I got it to work, and it worked fine-as long as I didn't try to format a column that was more than 64 characters wide. Then everything came out scrambled.

Whoops. I printed the whole thing out and sat down to do some serious debugging. Then I realized with a feeling of sinking horror that, having finished the last part of the program, I had no idea how the first part worked.

The APL symbol set was only part of the problem. I soon came to realize that the most important mistake I had made was writing the whole thing as one 600-line monolithic block of code lines. There were no functional divisions, nothing to indicate what any 10-line portion of the code was trying to accomplish.

The Martians had won. I did the only thing possible: I scrapped it. And I settled for ragged margins in my text.