2709	 A Genealogy of Control Structures	 The issue of program control structures has had a history of heated controversy. To put this issue on a solid footing this paper reviews numerous theoretical results on control structures and explores their practical implications. The classic result of Bohm and Jacopini on the theoretical completeness of if-then-else and while-do is discussed. Several recent ideas on control structures are then explored. These include a review of various other control structures results on time space limitations and theorems relating the relative power of control structures under notions of equivalence. In conclusion the impact of theoretical results on the practicing programmer and the importance of one-in one-out control structures as operational abstractions are discussed. It is argued further that there is insufficient evidence to warrant more than if-then-else while-do and their variants. structured programming control structures goto statements language design PASCAL
