Since our last issue weve lost our most valued reader, Dr Kenneth E. Iverson. Many people have contributed to APL, which is now several dialects; Ken Iverson was father to them all.
The ambiguity is deliberate. Many people have now expressed their gratitude for the gift of these languages, from which we have paying work that remains a recurrent source of pleasure. And many have expressed their gratitude for the gift of Ken Iversons teaching.
A quarter of a century ago in London he taught a course for APL instructors. I learned from him that I had to take myself out of the learning process: my biggest obstacle to teaching effectively is my own desire to teach, to be the man with the answers. (This must have been the Albertan school of Zen.) When a student asked why 2*3 gives the wrong answer, I was not to explain the difference between the times and power functions, but ask instead what the answer should have been, and through Kens famous use of Socratic method lead the student to identify and revise the false premise. Kens ideal of a teacher was not the man with all the answers, but an irritating and provocative Socrates, one part guide, three parts goad.
I learned to appreciate and eventually to share his fierce, wolfish joy at seeing a student find his own way to a larger understanding. It was a life-changing lesson, which I later took with me into psychotherapy.
Play that pays: Ken Iverson blessed those of us who program in the APLs with paying work that is also study and play. VECTOR 21.2 will celebrate his life and work; this issue is rich in games and puzzles.
Besides our regular crossword puzzle, Brian Schott writes on using J to construct them. Roger Hui rescales the venerable Tower of Hanoi with J, and Devon McCormick tackles the Monty Hall problem in APL. Michael Horton translates his fascination with Celtic knotwork into disarmingly simple J verbs. Eugene McDonnell found a puzzle set by Google to catch engineers, and sets about it solving it with J. Norman Thomson follows Eugenes recent article on word ladder puzzles with algorithms to find short paths through graphs.
In our technical section Dan Baronet continues his series on development tools, and David Crossley offers more thoughts on execute inverse. He also describes how to launch an APL workspace, and Richard Hill describes how to use J notation in Excel as an alternative to learning a lot of verbose VBA you might prefer not to know.