Abstractions All The Way

Abstract

Creative people are driven by certain inner forces, inner needs that are part cognitive, part affective. One such force is intellectual curiosity: the need to know or understand. Another compelling drive is dissatisfaction with the status quo. We saw this as the force that impelled Nicklaus Wirth into creating Pascal (Chapter 1, Section 1.7). But few in the emerging computer science community of the first age of computer science epitomized this characteristic more fiercely than Edsger W. Dijkstra. In his case his discontent was with the direction programming had taken in the 1960s. And the strength of his dissat­isfaction was never more evident than in a letter to the editor of the Communications of the ACM in 1968. The practice of communicating new scientific results by their discoverers in the form of compact letters to the editors of scientific journals was, of course, well established in the natural sciences. The British journal Nature (London) had established this tradition right from its inaugural issue in 1869. But in an upstart discipline, as computer science still was, this practice as a means of scientific communication was quite un­usual. (In one of his celebrated handwritten “EWD notes,” Dijkstra, reflecting retrospectively, explained that his short paper was published as a letter to bypass the usual publication pipeline and that the editor who made this decision was Nicklaus Wirth.) Dijkstra had long been concerned with the question of program quality and how one may acquire confidence in the reliability or correctness of a program. But, as the title of the letter— “Goto Statement Considered Harmful”— tells us, the object of his discontent lay in the use of the goto statement— the unconditional branch available in one notation or another in most programming languages, including Algol-like ones. Dijkstra claimed that the quality of the programmers decreased as a function of the frequency of the goto statements in their programs. And so he proposed that the goto should be banished from all high- level programming languages.