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.
CACM November, 1975
Ledgard, H. F.
Marcotty, M.
