APL is more French than English

Almost Perfect Artifacts Improve only in Small Ways: APL is more French than English Professor Alan J. Perlis Yale University I’m an apostate from ALGOL. Having been raised on programming languages of the ALGOL variety, I came under the influence of APL rather late in life. Like all people who enter interesting things late in life, one tends to go over one’s head very quickly. I think it might be interesting to say how I came under the influence of APL, because maybe many of you have gone the same route. I was at a meeting in Newcastle, England, where I’d been invited to give a talk, as had Don Knuth of Stanford, Ken Iverson from IBM, and a few others as well. I was sitting in the audience sandwiched between two very esteemed people in computer science and computing — Fritz Bauer, who runs computing in Bavaria from his headquarters in Munich, and Edsger Dijkstra, who runs computing all over the world from his headquarters in Holland. Ken was showing some slides — and one of his slides had something on it that I was later to learn was an APL one-liner. And he tossed this off as an example of the expressiveness of the APL notation. I believe the one-liner was one of the standard ones for indicating the nesting level of the parentheses in an algebraic expression. But the one-liner was very short — ten characters, something like that — and having been involved with programming things like that for a long time and realizing that it took a reasonable amount of code to do, I looked at it and said, “My God, there must be something in this language.” Bauer, on my left, didn’t see that. What he saw or heard was Ken’s remark that APL is an extremely appropriate language for teaching algebra, and he muttered under his breath to me, in words I will never forget, “As long as I am alive, APL will never be used in Munich.” And Dijkstra, who was sitting on my other side, leaned toward Bauer and said, “Nor in Holland.” The three of us were listening to the same lecture, but we obviously heard different things. What attracted me, then, to APL was a feeling that perhaps through APL one might begin to acquire some of the dimensions in programming that we revere in natural language — some of the pleasures of composition; of saying things elegantly; of being brief, poetic, artistic, that makes our natural languages so precious to us. That aspect of programming was one that I’ve long been interested in but have never found any level for coming close to in my experience with languages of the FORTRAN, ALGOL, PL/I school. It was clear in those languages that programming was really an exercise in plumbing. One was building an intricate object, and the main problem was just to keep your head above water. But, so difficult is it to keep your head above water with those languages that this aspect of the languages we use in programming just never surfaces. For me, in listening to Ken then — and I’d heard him before — for me, at that moment, there came what I can only call a revelation. I heard Ken speak in 1963 at Princeton at a meeting on programming languages, and he spoke about APL. But at that time APL was not running on any computer; and he stoutly insisted that it was unnecessary that it ever run on a computer. It was for him a notation with which he could express algorithmic concepts; and for him at that time, that seemed sufficient. To those of us who were concerned with making programs work on real computers, this seemed far short of the mark. Some years…

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