Masterminds of Programming

Chapter 3. APL

In the late 1950s, while on the faculty of Harvard University, Kenneth Iverson devised an extension of mathematical notation for the precise description of algorithms. Then, along with Adin Falkoff and other researchers at IBM, the team gradually turned the notation into a full-fledged programming language called APL. The language uses an extended character set requiring a specialized keyboard and appears on the page as strings of sometimes unfamiliar symbols—but the underlying consistency of the language makes it easy to learn, and its unmatched array-processing capabilities make it extraordinarily powerful. Its spiritual descendents, J and K, continue APL’s legacy of concise and powerful algebraic manipulations.

Paper and Pencil

I read a paper written by you and Ken Iverson, “The Design of APL,” which said that the first seven or eight years of development happened without any computer involved! This let you change design aspects without having to worry about legacy issues. How did the first software implementation influence the evolution of the language?

Adin Falkoff: Yes, the first years of the evolution of APL, when it had no name other than “Iverson’s notation,” were mainly concerned with paper-and-pencil mathematical applications, analysis of digital systems, and teaching. To a great extent, we thought of programming as a branch of mathematics concerned with the discovery and design of algorithms, and this concept was supported by the symbolic form of the ...