8 Aug 2002 raph   » (Master)

In memoriam, Edsger Dijkstra

Yesterday night, Edsger Dijkstra died of cancer. His early work was truly pioneering, with many of his ideas forming an integral part of computing today, including semaphores. He perhaps most famous for his article, "Go To Statement Considered Harmful". Since then, "considered harmful" has become a distinctive part of the computing lexicon.

Dijkstra was an intellectual father to me. Twenty or so years ago, my father initiated a correspondence with him, and we kept it up for some years. I eagerly awaited the airmail envelope from Holland, addressed beautifully in fountain pen, and always found the contents to be equally beautiful, in words as well as penmanship. It's remarkable that he took time in his busy life to correspond with an arrogant young kid, and I still appreciate it.

Later, I attended the 1990 Marktoberdorf summer school, and had a chance to experience Dijkstra's wit, charm, and warmth. Looking back, it was a key point in my life - I was struggling with what direction it should take. The summer school was an amazingly stimulating and positive experience in academic computer science, and no doubt contributed to my decision to enter graduate school at Berkeley two years later.

I have been deeply influenced by his work on formal techniques. I haven't proved any real programs correct, but very often, thinking "how would I prove this correct?" has led to a better solution. His exposition of weakest preconditions was an intellectual delight, providing deep insight into the basic stuff that programs are made of.

Dijkstra possessed a bright, clear vision of how we should program. To him, programs were theorems, and programming was essentially the same as working out proofs. Over time, he developed a distinct style of writing proofs, emphasizing simplicity and straightforward application of steps.

Today, his vision is, sadly, still exciting and bold. In a more perfect world, the computer industry would have embraced his ideas, and much programming today would be organized around writing provably correct programs. Many of Dijkstra's beautiful, angry essays took the world to task for short-sightedness, upholding the ideals of intellectual rigor and simple, systematic design.

His formal techniques and style have not become wildly popular, but I believe they have been deeply influential nonetheless, through his patient teaching and clear writing. I am sure that when, some day, computing progresses from its current crude, alchemical practice to a real science, it will resemble Dijkstra's vision, and published work, much more closely than the bloated, corporate-designed messes we're saddled with today.

Now that Dijkstra has passed on, it falls to our generation to carry his ideals forward. Let us strive for simplicity in all our work. Let us strive to choose the right path, even when a shortcut seems more expedient.

Calculemus!

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