My diary on what Dijkstra did in the 1970s.

Letter from Wirth to Dijkstra


19 March 1971

Wirth and Dijkstra were close colleagues, thoroughly studying each other's writings in 1971. But how close, exactly, were they? How did Wirth's views differ from those of Dijkstra? In my first attempt to address these matters, I shall discuss a letter Wirth sent to Dijkstra in March 1971.


Five elements of mental discipline.

One of Dijkstra's main questions was:

"Can the programmer arrange his activity in such a way that his growing product remains firmly in his intellectual grip, that he continues to understand what he is doing?" [EWD303]

To write structured programs, Dijkstra proposed five well-known techniques:

  • sequencing
  • operational abstraction
  • representational abstraction
  • configurational abstraction (cf. layered software)
  • textual encapsulation (cf. modularity)

The latter two are discussed here.


Humble with regard to virtual storage.

Looking back at the late 1960s, Dijkstra mentioned that progress had been made in processor allocation, mainly due to the work of his students Bomhoff and Feijen. With respect to virtual storage implementations, however, Dijkstra humbly admitted that much had still to be done on this subject. Even though he had spent months trying to do so, he was stil not able to find the right abstractions. [EWD300]



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