BIT 9(3): 250-258, 1969.

Commentary 1990

The original version of this paper has been the target of justified criticism, in view of the fact that the program developed in section 5.3.5 as the demonstration of the technique had an error, in that it inserted a spurious BLANK before the first word in the first line. In the present version this error has been corrected. However no attempt has been made to extend the solution so as to cater for arbitrary input, and neither has the omission of a suitable termination of the process has been corrected, on the ground that the idea of the paper, action clusters, is sufficiently displayed even without such refinements.


The paper describes a programming discipline, aiming at the systematic construction of programs from given global requirements. The crucial step in the approach is the conversion of the global requirements into sets of action clusters (sequences of program statements), which are then used as building blocks for the final program. The relation of the approach to proof techniques and to programming languages is discussed briefly.