Abstraction and verification in Alphard: defining and specifying iteration and generators

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Conference Proceeding

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Abstract or Description

The Alphard “form” provides the programmer with a great deal of control over the implementation of abstract data types. In this paper the abstraction techniques are extended from simple data representation and function definition to the iteration statement, the most important point of interaction between data and the control structure of the language itself. A means of specializing Alphard's loops to operate on abstract entities without explicit dependence on the representation of those entities is introduced. Specification and verification techniques that allow the properties of the generators for such iterations to be expressed in the form of proof rules are developed. Results are obtained that for common special cases of these loops are essentially identical to the corresponding constructs in other languages. A means of showing that a generator will terminate is also provided.




Presented at ACM Conference on Language Design for Reliable Software, March 1977. Reprinted in Tutorial: Programming Language Design, text for IEEE Tutorial by Anthony I. Wasserman, 1980, pp.145-155. Original report reprinted in Alphard: Form and Content (Mary Shaw, ed), Springer-Verlag 1981.