Abstract
A new control structure construct, thewhile-until, is introduced as a syntactic combination of thewhile statement and therepeat-until statement. Examples show that the use of thewhile-until can lead to structured programs that are conceptually more manageable than those attainable without it. Thewhile-until statement is then extended to a value-returning expression which is shown to be more powerful than the classical looping structures. It is shown to be equivalent in power to those structures withexit when a value-returningif-then-else is allowed. As a consequence, there are flowcharts whose implementations require control structures stronger than thewhile-until. Implementation details are discussed and Hoare-like axioms are presented. A closing discussion on oesthetics discourages some natural generalizations, but it concludes that the basicwhile-until is convenient for all parties on a programming team: coder, reader, compiler, and validator.
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