Communications of the ACM
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An analysis of several routines from a large real time software system, using recently developed functional programming theory, has shown that the functional capabilities of the routines can be constructed from analysis of the code text. This analysis also showed that the number of distinct functions computed by a program is much smaller than generally appreciated. Many apparent logic paths are not executable, some executable logic paths compute the same function (on different input subsets), and some functions are unnecessarily fragmented by excessive logic tests. With the aid of information derived from the analysis, the routines were restructured into simpler forms, having fewer executable statements and a more visible relationship of code text to functional capabilities. Some of the restructured routines have higher performance-shorter execution time and less primary storage usage. The application of functional programming to the generation of test cases to demonstrate satisfaction of functional requirements, software maintenance, and construction of new programs having visible correspondence to functional requirements is also discussed.