Edsger W. Dijkstra: Difference between revisions

'''Edsger Wybe Dijkstra''' was a pioneering computer scientist particularly interested in using mathematical proof to produce correct programs. In programming language design he is noted for early advocacy against the GOTO statement (like APL's [[branch]]) in his 1968 paper "A Case against the GO TO Statement", later retitled "Go To Statement Considered Harmful"<ref>Dijkstra, E.W. [http://www.cs.utexas.edu/users/EWD/transcriptions/EWD02xx/EWD215.html EWD 215: A Case against the GO TO Statement]</ref>. He is known in array programming for his consistent complaints against the APL language and community.

There is no evidence that Dijkstra was ever a user of APL, and several of his remarks suggest he would refuse any opportunity to use or learn it. His familiarity with the language comes from attending presentations by [[Ken Iverson]] and others, and friendship with [[Alan Perlis]], a fan of the language.

{{quote|Dijkstra: How would you represent a more complex operation, for example, the sum of all elements of a matrix M which are equal to the sum of the corresponding row and column indices?<br/>

* A typical characteristic of the APL devotee is, for instance, his closeness to an implementation of it. I know of a visiting professor at an American University [sic] who, trying to teach APL, bitterly complained about the absence of APL terminals. He was clearly unable to teach it without them. And you, too, write to me that you would like to meet me in your part of the world, so that you can “demonstrate APL” to me. This is in sharp contrast to people who prefer programming languages that can be adadequately [sic] “demonstrated”—i.e. shown, taught and discussed—with pencil and paper.

{{Quote|What [Fritz Bauer] 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.}}

* [https://www.jsoftware.com/papers/TAOaxioms.htm "TAO Axioms"]

Dijkstra claims that APL is a "bag of tricks" which encourages the programmer to think of problems as merely puzzles which require them to find the correct trick rather than to approach them by trying to express their ideas elegantly. An APLer would probably conclude that he has fallen into the trap of thinking of APL as a [[domain-specific language]] which just happens to have the right solution for the particular problem under consideration. Iverson thought instead that APLs tricks are carefully selected tools which guide programmers to more elegant solutions, and elegance is a primary concern for APL programmers today. This comment may also reflect a lack of introspection by Dijkstra into his own working methods and those of other mathematicians: mathematicians work by applying high-level concepts, techniques, or tricks, and write proofs by translating these tricks into mathematical language. APL aids a mathematician's thinking by supplying a well-considered set of techniques, and eases reading by making the "tricks" explicit rather than forcing the reader to extract them from a low-level notation.

Dijkstra's paper "Go To Statement Considered Harmful" was an important factor in the introduction of structured programming, which in APL has led to the addition of [[control structure]]s and encouraging their use in favor of the [[branch]] command. Papers on [https://link.springer.com/chapter/10.1007/3-540-07131-8_25 APLGOL] and [https://www.researchgate.net/publication/262210729_Design_of_a_structured_APL SAPL], two experiments in bringing structured programming to APL in the 1970s, both reference Dijkstra's work.

== External links ==

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